[PATCH v2 0/9] printk: Clean up preferred console handling

[PATCH v2 0/9] printk: Clean up preferred console handling

[Petr Mladek]

Hi,

this patchset does some clean up of the code for handling preferred consoles
in the console registration code.

  + 1st and 2nd patch try to improve some naming.

  + 3rd patch removes some code duplication. It better defines and describes
    the rules for adding and updating preferred consoles. It uses a more
    defensive coding style.

  + 4th, 5th, 6th, and 7th patch improve handling of Braille consoles.
    They are preferred via the command line but they do not get
    printk() messages and are not associated with /dev/console.

    The new code makes this more obvious. Also it explicitly
    defines the relation against default consoles and other
    non-Braille preferred consoles.

  + 8th patch removes a hidden side effect of
    try_enable_preferred_console()

  + 9th patch removes the last hidden side effect of
    try_enable_preferred_console() and allows to call it
    only when there are any non-Braille preferred consoles.

This patchset is a prerequisite for Marcos' clean up of CON_ENABLE
flag handling. It should prevent regressions caused by the
hidden effects of try_enable_preferred_console(), for example,
see https://lore.kernel.org/r/89409a0f48e6998ff6dd2245691b9954f0e1e435.camel@suse.com

Also I am working on a feature which would allow to explicitly
enable/prefer consoles proposed by SPCR, device tree, or
platform-specific code using a generic "console=platform".
This clean up is a prerequisite, see
https://github.com/pmladek/linux/tree/console-platform-poc1-iter9

Changes against [v1]:

  + Fix stale comment (1st patch, Chris)

  + Add comment descibing update_preferred_console() behavior (3rd patch, John)

  + Better describe behavior changes caused by update_preferred_console()
    in the commit message (3rd patch, Chris)

  + Use unsigned int for iterating/indexing preferred_consoles[]
    table (3rd patch, John)

  + Add a check preventing an update via "devname" is already assigned
    to a real "name". (3rd patch, Petr)

  + Use only Braille entries when trying to enable Braille console (Chris)

  + Split all try_enable_*console() calls into new try_enable_console()
    and return early when try_enable_braille_console() succeeded.
    Note that we do not longer need to initialize "err" variable
    in this case. (new 5th patch, Chris, Petr)

  + Put back the explicit check of CON_BRL flag in register_console()
    so that it returns prelimitary only when the driver is used in Braille
    mode. (6th patch, Chris, Petr)

  + Add comments explaining that try_enable_braille_console() might succeeded
    also when newcon->match() succeeded. In this case, the Braille mode can't
    be used because the console device was already used as an early console.[*]
    (6th patch, Chris, Petr)

  + Reset preferred_dev_console_prev when used to revert the value.
    (7th patch, John)

  + Add Acked-by and Reviewed-by tags (1st, 2nd, 4th patch, Chris, Marcos)

[*] This is a questional behavior. I would personally prefer when
    the early console is unregistered at this point and the console
    device is converted into Braille console. I consider the Braille
    mode more important. But it might be changed/fixed later
    in another patchset.

[v1] https://lore.kernel.org/r/20260206165002.496724-1-pmladek@suse.com


Petr Mladek (9):
  printk: Rename struct console_cmdline to preferred_console
  printk: Rename preferred_console to preferred_dev_console
  printk: Separate code for adding/updating preferred console metadata
  printk: Cleanup _braille_(un)register_console() wrappers
  printk: Separate code for enabling console
  printk: Try to register each console as Braille first
  printk: Do not set Braille console as preferred_console
  printk: Handle pre-enabled consoles in the top-level
    try_enable_console()
  printk: Try enable preferred consoles only when there are any

 .../accessibility/braille/braille_console.c   |   7 +-
 kernel/printk/braille.c                       |  20 +-
 kernel/printk/braille.h                       |  23 +-
 .../{console_cmdline.h => console_register.h} |   6 +-
 kernel/printk/printk.c                        | 390 ++++++++++++------
 5 files changed, 301 insertions(+), 145 deletions(-)
 rename kernel/printk/{console_cmdline.h => console_register.h} (83%)

-- 
2.53.0

[PATCH v2 1/9] printk: Rename struct console_cmdline to preferred_console

[Petr Mladek]

The structure 'console_cmdline' was originally intended to store details
about consoles defined on the kernel command line. However, its usage
has since expanded; it now stores information for consoles preferred
via SPCR, device tree, or by particular platforms, e.g. XEN.

The current naming is misleading as it implies the configuration only
originates from the command line.

Rename the structure and associated artifacts to better reflect their
current purpose, for example:

  - struct console_cmdline c -> struct preferred_console pc
  - console_cmdline[]        -> preferred_consoles[]
  - console_cmdline.h        -> console_register.h
  - c			     -> pc

Additionally, renaming the header file to console_register.h would
eventually allow to decouple console registration logic from
the monolithic printk.c.

Finally, renaming the local variable from "c" to "pc" helps to distinguish
it from struct console variables. Note that "c" is used for struct console
in some code, for example see vt_console_device() function definition.

The patch should not change the existing behaivor.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
Acked-by: Marcos Paulo de Souza <mpdesouza@suse.com>
---
 kernel/printk/braille.c                       | 10 +--
 kernel/printk/braille.h                       | 10 +--
 .../{console_cmdline.h => console_register.h} |  6 +-
 kernel/printk/printk.c                        | 86 ++++++++++---------
 4 files changed, 57 insertions(+), 55 deletions(-)
 rename kernel/printk/{console_cmdline.h => console_register.h} (83%)

diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
index 17a9591e54ff..9d21a2bb1d38 100644
--- a/kernel/printk/braille.c
+++ b/kernel/printk/braille.c
@@ -6,7 +6,7 @@
 #include <linux/errno.h>
 #include <linux/string.h>
 
-#include "console_cmdline.h"
+#include "console_register.h"
 #include "braille.h"
 
 int _braille_console_setup(char **str, char **brl_options)
@@ -35,14 +35,14 @@ int _braille_console_setup(char **str, char **brl_options)
 }
 
 int
-_braille_register_console(struct console *console, struct console_cmdline *c)
+_braille_register_console(struct console *console, struct preferred_console *pc)
 {
 	int rtn = 0;
 
-	if (c->brl_options) {
+	if (pc->brl_options) {
 		console->flags |= CON_BRL;
-		rtn = braille_register_console(console, c->index, c->options,
-					       c->brl_options);
+		rtn = braille_register_console(console, pc->index, pc->options,
+					       pc->brl_options);
 	}
 
 	return rtn;
diff --git a/kernel/printk/braille.h b/kernel/printk/braille.h
index 123154f86304..55cd3178a17a 100644
--- a/kernel/printk/braille.h
+++ b/kernel/printk/braille.h
@@ -5,9 +5,9 @@
 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 
 static inline void
-braille_set_options(struct console_cmdline *c, char *brl_options)
+braille_set_options(struct preferred_console *pc, char *brl_options)
 {
-	c->brl_options = brl_options;
+	pc->brl_options = brl_options;
 }
 
 /*
@@ -21,7 +21,7 @@ int
 _braille_console_setup(char **str, char **brl_options);
 
 int
-_braille_register_console(struct console *console, struct console_cmdline *c);
+_braille_register_console(struct console *console, struct preferred_console *pc);
 
 int
 _braille_unregister_console(struct console *console);
@@ -29,7 +29,7 @@ _braille_unregister_console(struct console *console);
 #else
 
 static inline void
-braille_set_options(struct console_cmdline *c, char *brl_options)
+braille_set_options(struct preferred_console *pc, char *brl_options)
 {
 }
 
@@ -40,7 +40,7 @@ _braille_console_setup(char **str, char **brl_options)
 }
 
 static inline int
-_braille_register_console(struct console *console, struct console_cmdline *c)
+_braille_register_console(struct console *console, struct preferred_console *pc)
 {
 	return 0;
 }
diff --git a/kernel/printk/console_cmdline.h b/kernel/printk/console_register.h
similarity index 83%
rename from kernel/printk/console_cmdline.h
rename to kernel/printk/console_register.h
index 0ab573b6d4dc..9ab3e1cc749b 100644
--- a/kernel/printk/console_cmdline.h
+++ b/kernel/printk/console_register.h
@@ -1,8 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _CONSOLE_CMDLINE_H
-#define _CONSOLE_CMDLINE_H
+#ifndef _CONSOLE_REGISTER_H
+#define _CONSOLE_REGISTER_H
 
-struct console_cmdline
+struct preferred_console
 {
 	char	name[16];			/* Name of the driver	    */
 	int	index;				/* Minor dev. to use	    */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 0323149548f6..ca523acbf58d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -58,7 +58,7 @@
 #include <trace/events/printk.h>
 
 #include "printk_ringbuffer.h"
-#include "console_cmdline.h"
+#include "console_register.h"
 #include "braille.h"
 #include "internal.h"
 
@@ -362,9 +362,9 @@ static int console_locked;
  *	Array of consoles built from command line options (console=)
  */
 
-#define MAX_CMDLINECONSOLES 8
+#define MAX_PREFERRED_CONSOLES 8
 
-static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
+static struct preferred_console preferred_consoles[MAX_PREFERRED_CONSOLES];
 
 static int preferred_console = -1;
 int console_set_on_cmdline;
@@ -2544,16 +2544,16 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
 }
 #endif
 
-static void set_user_specified(struct console_cmdline *c, bool user_specified)
+static void set_user_specified(struct preferred_console *pc, bool user_specified)
 {
 	if (!user_specified)
 		return;
 
 	/*
-	 * @c console was defined by the user on the command line.
+	 * @pc console was defined by the user on the command line.
 	 * Do not clear when added twice also by SPCR or the device tree.
 	 */
-	c->user_specified = true;
+	pc->user_specified = true;
 	/* At least one console defined by the user on the command line. */
 	console_set_on_cmdline = 1;
 }
@@ -2562,7 +2562,7 @@ static int __add_preferred_console(const char *name, const short idx,
 				   const char *devname, char *options,
 				   char *brl_options, bool user_specified)
 {
-	struct console_cmdline *c;
+	struct preferred_console *pc;
 	int i;
 
 	if (!name && !devname)
@@ -2581,30 +2581,30 @@ static int __add_preferred_console(const char *name, const short idx,
 	 *	See if this tty is not yet registered, and
 	 *	if we have a slot free.
 	 */
-	for (i = 0, c = console_cmdline;
-	     i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
-	     i++, c++) {
-		if ((name && strcmp(c->name, name) == 0 && c->index == idx) ||
-		    (devname && strcmp(c->devname, devname) == 0)) {
+	for (i = 0, pc = preferred_consoles;
+	     i < MAX_PREFERRED_CONSOLES && (pc->name[0] || pc->devname[0]);
+	     i++, pc++) {
+		if ((name && strcmp(pc->name, name) == 0 && pc->index == idx) ||
+		    (devname && strcmp(pc->devname, devname) == 0)) {
 			if (!brl_options)
 				preferred_console = i;
-			set_user_specified(c, user_specified);
+			set_user_specified(pc, user_specified);
 			return 0;
 		}
 	}
-	if (i == MAX_CMDLINECONSOLES)
+	if (i == MAX_PREFERRED_CONSOLES)
 		return -E2BIG;
 	if (!brl_options)
 		preferred_console = i;
 	if (name)
-		strscpy(c->name, name);
+		strscpy(pc->name, name);
 	if (devname)
-		strscpy(c->devname, devname);
-	c->options = options;
-	set_user_specified(c, user_specified);
-	braille_set_options(c, brl_options);
+		strscpy(pc->devname, devname);
+	pc->options = options;
+	set_user_specified(pc, user_specified);
+	braille_set_options(pc, brl_options);
 
-	c->index = idx;
+	pc->index = idx;
 	return 0;
 }
 
@@ -2624,8 +2624,10 @@ __setup("console_msg_format=", console_msg_format_setup);
  */
 static int __init console_setup(char *str)
 {
-	static_assert(sizeof(console_cmdline[0].devname) >= sizeof(console_cmdline[0].name) + 4);
-	char buf[sizeof(console_cmdline[0].devname)];
+	static_assert(sizeof(preferred_consoles[0].devname) >=
+		      sizeof(preferred_consoles[0].name) + 4);
+
+	char buf[sizeof(preferred_consoles[0].devname)];
 	char *brl_options = NULL;
 	char *ttyname = NULL;
 	char *devname = NULL;
@@ -2730,19 +2732,19 @@ int match_devname_and_update_preferred_console(const char *devname,
 					       const char *name,
 					       const short idx)
 {
-	struct console_cmdline *c = console_cmdline;
+	struct preferred_console *pc = preferred_consoles;
 	int i;
 
 	if (!devname || !strlen(devname) || !name || !strlen(name) || idx < 0)
 		return -EINVAL;
 
-	for (i = 0; i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
-	     i++, c++) {
-		if (!strcmp(devname, c->devname)) {
+	for (i = 0; i < MAX_PREFERRED_CONSOLES && (pc->name[0] || pc->devname[0]);
+	     i++, pc++) {
+		if (!strcmp(devname, pc->devname)) {
 			pr_info("associate the preferred console \"%s\" with \"%s%d\"\n",
 				devname, name, idx);
-			strscpy(c->name, name);
-			c->index = idx;
+			strscpy(pc->name, name);
+			pc->index = idx;
 			return 0;
 		}
 	}
@@ -3897,33 +3899,33 @@ static int console_call_setup(struct console *newcon, char *options)
 static int try_enable_preferred_console(struct console *newcon,
 					bool user_specified)
 {
-	struct console_cmdline *c;
+	struct preferred_console *pc;
 	int i, err;
 
-	for (i = 0, c = console_cmdline;
-	     i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
-	     i++, c++) {
+	for (i = 0, pc = preferred_consoles;
+	     i < MAX_PREFERRED_CONSOLES && (pc->name[0] || pc->devname[0]);
+	     i++, pc++) {
 		/* Console not yet initialized? */
-		if (!c->name[0])
+		if (!pc->name[0])
 			continue;
-		if (c->user_specified != user_specified)
+		if (pc->user_specified != user_specified)
 			continue;
 		if (!newcon->match ||
-		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
+		    newcon->match(newcon, pc->name, pc->index, pc->options) != 0) {
 			/* default matching */
-			BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
-			if (strcmp(c->name, newcon->name) != 0)
+			BUILD_BUG_ON(sizeof(pc->name) != sizeof(newcon->name));
+			if (strcmp(pc->name, newcon->name) != 0)
 				continue;
 			if (newcon->index >= 0 &&
-			    newcon->index != c->index)
+			    newcon->index != pc->index)
 				continue;
 			if (newcon->index < 0)
-				newcon->index = c->index;
+				newcon->index = pc->index;
 
-			if (_braille_register_console(newcon, c))
+			if (_braille_register_console(newcon, pc))
 				return 0;
 
-			err = console_call_setup(newcon, c->options);
+			err = console_call_setup(newcon, pc->options);
 			if (err)
 				return err;
 		}
@@ -3938,7 +3940,7 @@ static int try_enable_preferred_console(struct console *newcon,
 	 * without matching. Accept the pre-enabled consoles only when match()
 	 * and setup() had a chance to be called.
 	 */
-	if (newcon->flags & CON_ENABLED && c->user_specified ==	user_specified)
+	if (newcon->flags & CON_ENABLED && pc->user_specified == user_specified)
 		return 0;
 
 	return -ENOENT;
-- 
2.53.0

Re: [PATCH v2 1/9] printk: Rename struct console_cmdline to preferred_console

[Steven Rostedt]

On Thu, 23 Apr 2026 15:00:06 +0200
Petr Mladek <pmladek@suse.com> wrote:

> The structure 'console_cmdline' was originally intended to store details
> about consoles defined on the kernel command line. However, its usage
> has since expanded; it now stores information for consoles preferred
> via SPCR, device tree, or by particular platforms, e.g. XEN.
> 
> The current naming is misleading as it implies the configuration only
> originates from the command line.
> 
> Rename the structure and associated artifacts to better reflect their
> current purpose, for example:
> 
>   - struct console_cmdline c -> struct preferred_console pc
>   - console_cmdline[]        -> preferred_consoles[]
>   - console_cmdline.h        -> console_register.h
>   - c			     -> pc

Nice.

> 
> Additionally, renaming the header file to console_register.h would
> eventually allow to decouple console registration logic from
> the monolithic printk.c.
> 
> Finally, renaming the local variable from "c" to "pc" helps to distinguish
> it from struct console variables. Note that "c" is used for struct console
> in some code, for example see vt_console_device() function definition.
> 
> The patch should not change the existing behaivor.

I believe the phrase is: "No functional changes" ;-)

> 
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> Acked-by: Chris Down <chris@chrisdown.name>
> Acked-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> ---


> @@ -2624,8 +2624,10 @@ __setup("console_msg_format=", console_msg_format_setup);
>   */
>  static int __init console_setup(char *str)
>  {
> -	static_assert(sizeof(console_cmdline[0].devname) >= sizeof(console_cmdline[0].name) + 4);
> -	char buf[sizeof(console_cmdline[0].devname)];
> +	static_assert(sizeof(preferred_consoles[0].devname) >=
> +		      sizeof(preferred_consoles[0].name) + 4);

Hmm with the line break and you adding a space before the declarations; If
this is going to change, might as well move it below the declarations as it
is a compile time check, and the order doesn't matter.

> +
> +	char buf[sizeof(preferred_consoles[0].devname)];
>  	char *brl_options = NULL;
>  	char *ttyname = NULL;
>  	char *devname = NULL;

-- Steve

Re: [PATCH v2 1/9] printk: Rename struct console_cmdline to preferred_console

[John Ogness]

On 2026-04-23, Petr Mladek <pmladek@suse.com> wrote:
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 0323149548f6..ca523acbf58d 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2624,8 +2624,10 @@ __setup("console_msg_format=", console_msg_format_setup);
>   */
>  static int __init console_setup(char *str)
>  {
> -	static_assert(sizeof(console_cmdline[0].devname) >= sizeof(console_cmdline[0].name) + 4);
> -	char buf[sizeof(console_cmdline[0].devname)];
> +	static_assert(sizeof(preferred_consoles[0].devname) >=
> +		      sizeof(preferred_consoles[0].name) + 4);
> +
> +	char buf[sizeof(preferred_consoles[0].devname)];

I agree with Steven's suggestion to move the static_assert() below the
local variable definitions.

Reviewed-by: John Ogness <john.ogness@linutronix.de>

[PATCH v2 2/9] printk: Rename preferred_console to preferred_dev_console

[Petr Mladek]

The preferred_consoles[] array stores information about consoles requested
via the command line, SPCR, Device Tree, or platform-specific code.
Within this array, the 'preferred_console' variable tracks the specific
index that should be associated with /dev/console (typically the last
non-braille console defined).

The current name "preferred_console" is ambiguous and leads to confusion.
It does not clearly communicate why one console is "more preferred" than
others in the array. Furthermore, entries for Braille consoles can exist
within the preferred_consoles[] array, yet they are never associated with
/dev/console and do not receive standard printk() output. Consequently,
the 'preferred_console' index must skip these entries, which is not
immediately obvious from the name.

Rename the variable to 'preferred_dev_console' to explicitly clarify its
role in identifying which entry is linked to /dev/console.

The patch should not change the existing behavior.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
Acked-by: Marcos Paulo de Souza <mpdesouza@suse.com>
---
 kernel/printk/printk.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ca523acbf58d..13c98285892b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -366,7 +366,7 @@ static int console_locked;
 
 static struct preferred_console preferred_consoles[MAX_PREFERRED_CONSOLES];
 
-static int preferred_console = -1;
+static int preferred_dev_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
@@ -2587,7 +2587,7 @@ static int __add_preferred_console(const char *name, const short idx,
 		if ((name && strcmp(pc->name, name) == 0 && pc->index == idx) ||
 		    (devname && strcmp(pc->devname, devname) == 0)) {
 			if (!brl_options)
-				preferred_console = i;
+				preferred_dev_console = i;
 			set_user_specified(pc, user_specified);
 			return 0;
 		}
@@ -2595,7 +2595,7 @@ static int __add_preferred_console(const char *name, const short idx,
 	if (i == MAX_PREFERRED_CONSOLES)
 		return -E2BIG;
 	if (!brl_options)
-		preferred_console = i;
+		preferred_dev_console = i;
 	if (name)
 		strscpy(pc->name, name);
 	if (devname)
@@ -3930,7 +3930,7 @@ static int try_enable_preferred_console(struct console *newcon,
 				return err;
 		}
 		newcon->flags |= CON_ENABLED;
-		if (i == preferred_console)
+		if (i == preferred_dev_console)
 			newcon->flags |= CON_CONSDEV;
 		return 0;
 	}
@@ -4111,7 +4111,7 @@ void register_console(struct console *newcon)
 	 * Note that a console with tty binding will have CON_CONSDEV
 	 * flag set and will be first in the list.
 	 */
-	if (preferred_console < 0) {
+	if (preferred_dev_console < 0) {
 		if (hlist_empty(&console_list) || !console_first()->device ||
 		    console_first()->flags & CON_BOOT) {
 			try_enable_default_console(newcon);
-- 
2.53.0

Re: [PATCH v2 2/9] printk: Rename preferred_console to preferred_dev_console

[John Ogness]

On 2026-04-23, Petr Mladek <pmladek@suse.com> wrote:
> The preferred_consoles[] array stores information about consoles requested
> via the command line, SPCR, Device Tree, or platform-specific code.
> Within this array, the 'preferred_console' variable tracks the specific
> index that should be associated with /dev/console (typically the last
> non-braille console defined).
>
> The current name "preferred_console" is ambiguous and leads to confusion.
> It does not clearly communicate why one console is "more preferred" than
> others in the array. Furthermore, entries for Braille consoles can exist
> within the preferred_consoles[] array, yet they are never associated with
> /dev/console and do not receive standard printk() output. Consequently,
> the 'preferred_console' index must skip these entries, which is not
> immediately obvious from the name.
>
> Rename the variable to 'preferred_dev_console' to explicitly clarify its
> role in identifying which entry is linked to /dev/console.
>
> The patch should not change the existing behavior.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> Acked-by: Chris Down <chris@chrisdown.name>
> Acked-by: Marcos Paulo de Souza <mpdesouza@suse.com>

Reviewed-by: John Ogness <john.ogness@linutronix.de>

[PATCH v2 3/9] printk: Separate code for adding/updating preferred console metadata

[Petr Mladek]

The logic for adding or updating a preferred console is currently
duplicated within __add_preferred_console(), making the code difficult
to follow and prone to consistency issues.

Introduce update_preferred_console() to centralize the initialization
and updating of struct preferred_console entries. This refactoring
explicitly defines and enforces the following rules:

1. Console names and/or indexes are not set when a console is preferred
   via devname; these are resolved later during device matching.
2. Console names are only added alongside a valid index.
3. Only matching entries are updated.
4. Console and Braille options are never cleared. They are updated
   only via the command line.
5. The global 'preferred_dev_console' index and 'console_set_on_cmdline'
   flag are updated consistently.

Additionally, rename braille_set_options() to braille_update_options()
to better reflect its conditional behavior.

Behavior change:

The original code never updated the preferred console options
when it was preferred more times, e.g. via the command line
and/or some platform specific code, e.g. SPCR or device tree.

The new code explicitly allows to update the console options
when they are preferred over the command line.

It mostly worked even before but only because the command line was
processed early enough before handling SPCR, device tree, or other
platform specific init code.

The main behavior change is when the same console is preferred more
times on the command line. Newly, the later or Braille variant
wins. It is a more common and expected behavior.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/braille.h |   7 +-
 kernel/printk/printk.c  | 149 ++++++++++++++++++++++++++++++----------
 2 files changed, 118 insertions(+), 38 deletions(-)

diff --git a/kernel/printk/braille.h b/kernel/printk/braille.h
index 55cd3178a17a..0bdac303f8b1 100644
--- a/kernel/printk/braille.h
+++ b/kernel/printk/braille.h
@@ -5,9 +5,10 @@
 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 
 static inline void
-braille_set_options(struct preferred_console *pc, char *brl_options)
+braille_update_options(struct preferred_console *pc, char *brl_options)
 {
-	pc->brl_options = brl_options;
+	if (brl_options)
+		pc->brl_options = brl_options;
 }
 
 /*
@@ -29,7 +30,7 @@ _braille_unregister_console(struct console *console);
 #else
 
 static inline void
-braille_set_options(struct preferred_console *pc, char *brl_options)
+braille_update_options(struct preferred_console *pc, char *brl_options)
 {
 }
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 13c98285892b..d251bf8e104f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2544,18 +2544,119 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
 }
 #endif
 
-static void set_user_specified(struct preferred_console *pc, bool user_specified)
+/** update_preferred_console - Update a given entry in the preferred_consoles[]
+ *	table.
+ * @i: index of the entry in @preferred_consoles table which should get updated.
+ * @name: The name of the preferred console driver.
+ * @idx: Preferred console index, e.g. port number.
+ * @devname: The name of the preferred physical device.
+ * @options: Options used when setting up the console driver.
+ * @brl_options: Options used when setting up the console driver
+ *	as a braille console.
+ * @user_specified: True if preferred via the kernel command line.
+ *
+ * The function ensures that the given values are consistent. Also
+ * it updates some global variables which are used to make the right
+ * decisions in register_console().
+ *
+ * Rules:
+ *
+ *   1. Either @name and valid @idx OR @devname and @idx=-1 are allowed.
+ *	Note that a valid @name and @idx will get assigned later when
+ *	@devname matches during the device initialization.
+ *   2. Specify @brl_options if the console should be enabled as
+ *	a Braille console [*]
+ *   3. Only matching entries can be updated.
+ *   4. @options passed via the command line are used when the same
+ *	console is preferred also by some platform-specific code.
+ *
+ * [*] Braille console is using the mechanism for registering consoles
+ *     but it is very special. It is primarily used for user interaction
+ *     with the system. It neither gets printk() messages nor is associated
+ *     with /dev/console.
+ */
+static int update_preferred_console(unsigned int i,
+				    const char *name, const short idx,
+				    const char *devname, char *options,
+				    char *brl_options, bool user_specified)
 {
-	if (!user_specified)
-		return;
+	struct preferred_console *pc;
+
+	if (i >= MAX_PREFERRED_CONSOLES)
+		return -E2BIG;
+
+	pc = &preferred_consoles[i];
+
+	if (!name && !devname)
+		return -EINVAL;
+
+	if (devname) {
+		/*
+		 * A valid console name and index will get assigned when
+		 * a matching device gets registered.
+		 */
+		if (name) {
+			pr_err("Adding a preferred console devname with a hard-coded console name: %s, %s\n",
+			       devname, name);
+			return -EINVAL;
+		}
+		if (pc->name[0]) {
+			pr_err("Updating a preferred console entry with an already assigned console name via devname: %s, %s\n",
+			       devname, pc->name);
+			return -EINVAL;
+		}
+		if (idx != -1) {
+			pr_err("Adding a preferred console devname with a hard-coded index: %s, %d\n",
+			       devname, idx);
+			return -EINVAL;
+		}
+
+		if (!pc->devname[0]) {
+			strscpy(pc->devname, devname);
+			pc->index = idx;
+		} else if (strcmp(pc->devname, devname) != 0) {
+			pr_err("Updating a preferred console with an invalid devname: %s vs. %s\n",
+			       pc->devname, devname);
+			return -EINVAL;
+		}
+	}
+
+	if (name) {
+		/* A console name must be defined with a valid index. */
+		if (idx < 0) {
+			pr_err("Adding a preferred console with an invalid index: %s, %d\n",
+			       name, idx);
+			return -EINVAL;
+		}
+
+		if (!pc->name[0]) {
+			strscpy(pc->name, name);
+			pc->index = idx;
+		} else if (strcmp(pc->name, name) != 0 || pc->index != idx) {
+			pr_err("Updating a preferred console with an invalid name or index: %s%d vs. %s%d\n",
+			       pc->name, pc->index, name, idx);
+			return -EINVAL;
+		}
+	}
+
+	if (!pc->options || (user_specified && options))
+		pc->options = options;
+
+	braille_update_options(pc, brl_options);
+
+	if (!brl_options)
+		preferred_dev_console = i;
 
 	/*
 	 * @pc console was defined by the user on the command line.
 	 * Do not clear when added twice also by SPCR or the device tree.
 	 */
-	pc->user_specified = true;
-	/* At least one console defined by the user on the command line. */
-	console_set_on_cmdline = 1;
+	if (user_specified) {
+		pc->user_specified = true;
+		console_set_on_cmdline = 1;
+	}
+
+	return 0;
 }
 
 static int __add_preferred_console(const char *name, const short idx,
@@ -2563,19 +2664,11 @@ static int __add_preferred_console(const char *name, const short idx,
 				   char *brl_options, bool user_specified)
 {
 	struct preferred_console *pc;
-	int i;
+	unsigned int i;
 
 	if (!name && !devname)
 		return -EINVAL;
 
-	/*
-	 * We use a signed short index for struct console for device drivers to
-	 * indicate a not yet assigned index or port. However, a negative index
-	 * value is not valid when the console name and index are defined on
-	 * the command line.
-	 */
-	if (name && idx < 0)
-		return -EINVAL;
 
 	/*
 	 *	See if this tty is not yet registered, and
@@ -2584,28 +2677,14 @@ static int __add_preferred_console(const char *name, const short idx,
 	for (i = 0, pc = preferred_consoles;
 	     i < MAX_PREFERRED_CONSOLES && (pc->name[0] || pc->devname[0]);
 	     i++, pc++) {
-		if ((name && strcmp(pc->name, name) == 0 && pc->index == idx) ||
-		    (devname && strcmp(pc->devname, devname) == 0)) {
-			if (!brl_options)
-				preferred_dev_console = i;
-			set_user_specified(pc, user_specified);
-			return 0;
-		}
+		if (name && strcmp(pc->name, name) == 0 && pc->index == idx)
+			break;
+		if (devname && strcmp(pc->devname, devname) == 0)
+			break;
 	}
-	if (i == MAX_PREFERRED_CONSOLES)
-		return -E2BIG;
-	if (!brl_options)
-		preferred_dev_console = i;
-	if (name)
-		strscpy(pc->name, name);
-	if (devname)
-		strscpy(pc->devname, devname);
-	pc->options = options;
-	set_user_specified(pc, user_specified);
-	braille_set_options(pc, brl_options);
 
-	pc->index = idx;
-	return 0;
+	return update_preferred_console(i, name, idx, devname, options,
+					brl_options, user_specified);
 }
 
 static int __init console_msg_format_setup(char *str)
-- 
2.53.0

Re: [PATCH v2 3/9] printk: Separate code for adding/updating preferred console metadata

[Marcos Paulo de Souza]

On Thu, 2026-04-23 at 15:00 +0200, Petr Mladek wrote:
> The logic for adding or updating a preferred console is currently
> duplicated within __add_preferred_console(), making the code
> difficult
> to follow and prone to consistency issues.
> 
> Introduce update_preferred_console() to centralize the initialization
> and updating of struct preferred_console entries. This refactoring
> explicitly defines and enforces the following rules:
> 
> 1. Console names and/or indexes are not set when a console is
> preferred
>    via devname; these are resolved later during device matching.
> 2. Console names are only added alongside a valid index.
> 3. Only matching entries are updated.
> 4. Console and Braille options are never cleared. They are updated
>    only via the command line.
> 5. The global 'preferred_dev_console' index and
> 'console_set_on_cmdline'
>    flag are updated consistently.
> 
> Additionally, rename braille_set_options() to
> braille_update_options()
> to better reflect its conditional behavior.
> 
> Behavior change:
> 
> The original code never updated the preferred console options
> when it was preferred more times, e.g. via the command line
> and/or some platform specific code, e.g. SPCR or device tree.
> 
> The new code explicitly allows to update the console options
> when they are preferred over the command line.
> 
> It mostly worked even before but only because the command line was
> processed early enough before handling SPCR, device tree, or other
> platform specific init code.
> 
> The main behavior change is when the same console is preferred more
> times on the command line. Newly, the later or Braille variant
> wins. It is a more common and expected behavior.

Sorry for the late review. I just wanted to say that the improvement is
really great: documentation and code reorganization really improve the
code. It was too confusing and rather problematic to follow up.

Acked-by: Marcos Paulo de Souza <mpdesouza@suse.com>

> 
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---
>  kernel/printk/braille.h |   7 +-
>  kernel/printk/printk.c  | 149 ++++++++++++++++++++++++++++++--------
> --
>  2 files changed, 118 insertions(+), 38 deletions(-)
> 
> diff --git a/kernel/printk/braille.h b/kernel/printk/braille.h
> index 55cd3178a17a..0bdac303f8b1 100644
> --- a/kernel/printk/braille.h
> +++ b/kernel/printk/braille.h
> @@ -5,9 +5,10 @@
>  #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
>  
>  static inline void
> -braille_set_options(struct preferred_console *pc, char *brl_options)
> +braille_update_options(struct preferred_console *pc, char
> *brl_options)
>  {
> -	pc->brl_options = brl_options;
> +	if (brl_options)
> +		pc->brl_options = brl_options;
>  }
>  
>  /*
> @@ -29,7 +30,7 @@ _braille_unregister_console(struct console
> *console);
>  #else
>  
>  static inline void
> -braille_set_options(struct preferred_console *pc, char *brl_options)
> +braille_update_options(struct preferred_console *pc, char
> *brl_options)
>  {
>  }
>  
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 13c98285892b..d251bf8e104f 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2544,18 +2544,119 @@ asmlinkage __visible void early_printk(const
> char *fmt, ...)
>  }
>  #endif
>  
> -static void set_user_specified(struct preferred_console *pc, bool
> user_specified)
> +/** update_preferred_console - Update a given entry in the
> preferred_consoles[]
> + *	table.
> + * @i: index of the entry in @preferred_consoles table which should
> get updated.
> + * @name: The name of the preferred console driver.
> + * @idx: Preferred console index, e.g. port number.
> + * @devname: The name of the preferred physical device.
> + * @options: Options used when setting up the console driver.
> + * @brl_options: Options used when setting up the console driver
> + *	as a braille console.
> + * @user_specified: True if preferred via the kernel command line.
> + *
> + * The function ensures that the given values are consistent. Also
> + * it updates some global variables which are used to make the right
> + * decisions in register_console().
> + *
> + * Rules:
> + *
> + *   1. Either @name and valid @idx OR @devname and @idx=-1 are
> allowed.
> + *	Note that a valid @name and @idx will get assigned later
> when
> + *	@devname matches during the device initialization.
> + *   2. Specify @brl_options if the console should be enabled as
> + *	a Braille console [*]
> + *   3. Only matching entries can be updated.
> + *   4. @options passed via the command line are used when the same
> + *	console is preferred also by some platform-specific code.
> + *
> + * [*] Braille console is using the mechanism for registering
> consoles
> + *     but it is very special. It is primarily used for user
> interaction
> + *     with the system. It neither gets printk() messages nor is
> associated
> + *     with /dev/console.
> + */
> +static int update_preferred_console(unsigned int i,
> +				    const char *name, const short
> idx,
> +				    const char *devname, char
> *options,
> +				    char *brl_options, bool
> user_specified)
>  {
> -	if (!user_specified)
> -		return;
> +	struct preferred_console *pc;
> +
> +	if (i >= MAX_PREFERRED_CONSOLES)
> +		return -E2BIG;
> +
> +	pc = &preferred_consoles[i];
> +
> +	if (!name && !devname)
> +		return -EINVAL;
> +
> +	if (devname) {
> +		/*
> +		 * A valid console name and index will get assigned
> when
> +		 * a matching device gets registered.
> +		 */
> +		if (name) {
> +			pr_err("Adding a preferred console devname
> with a hard-coded console name: %s, %s\n",
> +			       devname, name);
> +			return -EINVAL;
> +		}
> +		if (pc->name[0]) {
> +			pr_err("Updating a preferred console entry
> with an already assigned console name via devname: %s, %s\n",
> +			       devname, pc->name);
> +			return -EINVAL;
> +		}
> +		if (idx != -1) {
> +			pr_err("Adding a preferred console devname
> with a hard-coded index: %s, %d\n",
> +			       devname, idx);
> +			return -EINVAL;
> +		}
> +
> +		if (!pc->devname[0]) {
> +			strscpy(pc->devname, devname);
> +			pc->index = idx;
> +		} else if (strcmp(pc->devname, devname) != 0) {
> +			pr_err("Updating a preferred console with an
> invalid devname: %s vs. %s\n",
> +			       pc->devname, devname);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	if (name) {
> +		/* A console name must be defined with a valid
> index. */
> +		if (idx < 0) {
> +			pr_err("Adding a preferred console with an
> invalid index: %s, %d\n",
> +			       name, idx);
> +			return -EINVAL;
> +		}
> +
> +		if (!pc->name[0]) {
> +			strscpy(pc->name, name);
> +			pc->index = idx;
> +		} else if (strcmp(pc->name, name) != 0 || pc->index
> != idx) {
> +			pr_err("Updating a preferred console with an
> invalid name or index: %s%d vs. %s%d\n",
> +			       pc->name, pc->index, name, idx);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	if (!pc->options || (user_specified && options))
> +		pc->options = options;
> +
> +	braille_update_options(pc, brl_options);
> +
> +	if (!brl_options)
> +		preferred_dev_console = i;
>  
>  	/*
>  	 * @pc console was defined by the user on the command line.
>  	 * Do not clear when added twice also by SPCR or the device
> tree.
>  	 */
> -	pc->user_specified = true;
> -	/* At least one console defined by the user on the command
> line. */
> -	console_set_on_cmdline = 1;
> +	if (user_specified) {
> +		pc->user_specified = true;
> +		console_set_on_cmdline = 1;
> +	}
> +
> +	return 0;
>  }
>  
>  static int __add_preferred_console(const char *name, const short
> idx,
> @@ -2563,19 +2664,11 @@ static int __add_preferred_console(const char
> *name, const short idx,
>  				   char *brl_options, bool
> user_specified)
>  {
>  	struct preferred_console *pc;
> -	int i;
> +	unsigned int i;
>  
>  	if (!name && !devname)
>  		return -EINVAL;
>  
> -	/*
> -	 * We use a signed short index for struct console for device
> drivers to
> -	 * indicate a not yet assigned index or port. However, a
> negative index
> -	 * value is not valid when the console name and index are
> defined on
> -	 * the command line.
> -	 */
> -	if (name && idx < 0)
> -		return -EINVAL;
>  
>  	/*
>  	 *	See if this tty is not yet registered, and
> @@ -2584,28 +2677,14 @@ static int __add_preferred_console(const char
> *name, const short idx,
>  	for (i = 0, pc = preferred_consoles;
>  	     i < MAX_PREFERRED_CONSOLES && (pc->name[0] || pc-
> >devname[0]);
>  	     i++, pc++) {
> -		if ((name && strcmp(pc->name, name) == 0 && pc-
> >index == idx) ||
> -		    (devname && strcmp(pc->devname, devname) == 0))
> {
> -			if (!brl_options)
> -				preferred_dev_console = i;
> -			set_user_specified(pc, user_specified);
> -			return 0;
> -		}
> +		if (name && strcmp(pc->name, name) == 0 && pc->index
> == idx)
> +			break;
> +		if (devname && strcmp(pc->devname, devname) == 0)
> +			break;
>  	}
> -	if (i == MAX_PREFERRED_CONSOLES)
> -		return -E2BIG;
> -	if (!brl_options)
> -		preferred_dev_console = i;
> -	if (name)
> -		strscpy(pc->name, name);
> -	if (devname)
> -		strscpy(pc->devname, devname);
> -	pc->options = options;
> -	set_user_specified(pc, user_specified);
> -	braille_set_options(pc, brl_options);
>  
> -	pc->index = idx;
> -	return 0;
> +	return update_preferred_console(i, name, idx, devname,
> options,
> +					brl_options,
> user_specified);
>  }
>  
>  static int __init console_msg_format_setup(char *str)

Re: [PATCH v2 3/9] printk: Separate code for adding/updating preferred console metadata

[John Ogness]

On 2026-04-23, Petr Mladek <pmladek@suse.com> wrote:
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 13c98285892b..d251bf8e104f 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2544,18 +2544,119 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
>  }
>  #endif
>  
> -static void set_user_specified(struct preferred_console *pc, bool user_specified)
> +/** update_preferred_console - Update a given entry in the preferred_consoles[]
> + *	table.

Perhaps the description should be:

Update or add a given entry in the preferred_consoles[] table.

If the caller didn't match an existing preferred_console, this function
is called to add a new entry. This is obvious if you are looking at the
caller, but it is not obvious at all if you are only looking at this
function, i.e. strscpy'ing in @name or @devname is the only clue that
you are dealing with a new entry.

> + * @i: index of the entry in @preferred_consoles table which should get updated.
> + * @name: The name of the preferred console driver.
> + * @idx: Preferred console index, e.g. port number.
> + * @devname: The name of the preferred physical device.
> + * @options: Options used when setting up the console driver.
> + * @brl_options: Options used when setting up the console driver
> + *	as a braille console.
> + * @user_specified: True if preferred via the kernel command line.
> + *
> + * The function ensures that the given values are consistent. Also
> + * it updates some global variables which are used to make the right
> + * decisions in register_console().
> + *
> + * Rules:
> + *
> + *   1. Either @name and valid @idx OR @devname and @idx=-1 are allowed.
> + *	Note that a valid @name and @idx will get assigned later when
> + *	@devname matches during the device initialization.
> + *   2. Specify @brl_options if the console should be enabled as
> + *	a Braille console [*]
> + *   3. Only matching entries can be updated.
> + *   4. @options passed via the command line are used when the same
> + *	console is preferred also by some platform-specific code.
> + *
> + * [*] Braille console is using the mechanism for registering consoles
> + *     but it is very special. It is primarily used for user interaction
> + *     with the system. It neither gets printk() messages nor is associated
> + *     with /dev/console.
> + */
> +static int update_preferred_console(unsigned int i,
> +				    const char *name, const short idx,
> +				    const char *devname, char *options,
> +				    char *brl_options, bool user_specified)
>  {
> -	if (!user_specified)
> -		return;
> +	struct preferred_console *pc;
> +
> +	if (i >= MAX_PREFERRED_CONSOLES)
> +		return -E2BIG;
> +
> +	pc = &preferred_consoles[i];
> +
> +	if (!name && !devname)
> +		return -EINVAL;

You are adding detailed error messages for all possible wrong calls
except for this on. Maybe this should be covered as well with:

	if (WARN_ON(!name && !devname))
		return -EINVAL;

> +	if (devname) {
> +		/*
> +		 * A valid console name and index will get assigned when
> +		 * a matching device gets registered.
> +		 */
> +		if (name) {
> +			pr_err("Adding a preferred console devname with a hard-coded console name: %s, %s\n",
> +			       devname, name);
> +			return -EINVAL;
> +		}
> +		if (pc->name[0]) {
> +			pr_err("Updating a preferred console entry with an already assigned console name via devname: %s, %s\n",
> +			       devname, pc->name);
> +			return -EINVAL;
> +		}
> +		if (idx != -1) {
> +			pr_err("Adding a preferred console devname with a hard-coded index: %s, %d\n",
> +			       devname, idx);
> +			return -EINVAL;
> +		}
> +
> +		if (!pc->devname[0]) {
> +			strscpy(pc->devname, devname);
> +			pc->index = idx;

This block is about setting the devname. Setting the index here as well
is copied code and well hidden. I would keep the index setting outside
the devname and name blocks (as it was previously).

> +		} else if (strcmp(pc->devname, devname) != 0) {
> +			pr_err("Updating a preferred console with an invalid devname: %s vs. %s\n",
> +			       pc->devname, devname);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	if (name) {
> +		/* A console name must be defined with a valid index. */
> +		if (idx < 0) {
> +			pr_err("Adding a preferred console with an invalid index: %s, %d\n",
> +			       name, idx);
> +			return -EINVAL;
> +		}
> +
> +		if (!pc->name[0]) {
> +			strscpy(pc->name, name);
> +			pc->index = idx;

Here is the copied code. This block is about setting the name.

> +		} else if (strcmp(pc->name, name) != 0 || pc->index != idx) {
> +			pr_err("Updating a preferred console with an invalid name or index: %s%d vs. %s%d\n",
> +			       pc->name, pc->index, name, idx);
> +			return -EINVAL;
> +		}
> +	}

I would put the index setting here as it is relevant regardless of how
the devname or name was updated.

	pc->index = idx;

With or without implementing my suggestions:

Reviewed-by: John Ogness <john.ogness@linutronix.de>

Re: [PATCH v2 3/9] printk: Separate code for adding/updating preferred console metadata

[John Ogness]

On 2026-05-15, John Ogness <john.ogness@linutronix.de> wrote:
>> +		if (!pc->name[0]) {
>> +			strscpy(pc->name, name);
>> +			pc->index = idx;
>
> Here is the copied code. This block is about setting the name.
>
>> +		} else if (strcmp(pc->name, name) != 0 || pc->index != idx) {
>> +			pr_err("Updating a preferred console with an invalid name or index: %s%d vs. %s%d\n",
>> +			       pc->name, pc->index, name, idx);
>> +			return -EINVAL;
>> +		}
>> +	}
>
> I would put the index setting here as it is relevant regardless of how
> the devname or name was updated.
>
> 	pc->index = idx;

Ah, I guess you only wanted to update @index if it is a new entry
(because otherwise it will already have the value of @idx).

If you want to keep the index setting in the devname and name blocks,
maybe just adding a comment to clarify it is a new entry:

	if (!pc->devname[0]) {
		/* This is a new entry */
		strscpy(pc->devname, devname);
		pc->index = idx;

...

	if (!pc->name[0]) {
		/* This is a new entry */
		strscpy(pc->name, name);
		pc->index = idx;

John

Re: [PATCH v2 3/9] printk: Separate code for adding/updating preferred console metadata

[Petr Mladek]

On Fri 2026-05-15 12:36:58, John Ogness wrote:
> On 2026-05-15, John Ogness <john.ogness@linutronix.de> wrote:
> >> +		if (!pc->name[0]) {
> >> +			strscpy(pc->name, name);
> >> +			pc->index = idx;
> >
> > Here is the copied code. This block is about setting the name.
> >
> >> +		} else if (strcmp(pc->name, name) != 0 || pc->index != idx) {
> >> +			pr_err("Updating a preferred console with an invalid name or index: %s%d vs. %s%d\n",
> >> +			       pc->name, pc->index, name, idx);
> >> +			return -EINVAL;
> >> +		}
> >> +	}
> >
> > I would put the index setting here as it is relevant regardless of how
> > the devname or name was updated.
> >
> > 	pc->index = idx;
> 
> Ah, I guess you only wanted to update @index if it is a new entry
> (because otherwise it will already have the value of @idx).

Exactly ;-)

> If you want to keep the index setting in the devname and name blocks,
> maybe just adding a comment to clarify it is a new entry:
> 
> 	if (!pc->devname[0]) {
> 		/* This is a new entry */
> 		strscpy(pc->devname, devname);
> 		pc->index = idx;
> 
> ...
> 
> 	if (!pc->name[0]) {
> 		/* This is a new entry */
> 		strscpy(pc->name, name);
> 		pc->index = idx;

I am going to add the comments in v3.

Best Regards,
Petr

Re: [PATCH v2 3/9] printk: Separate code for adding/updating preferred console metadata

[Petr Mladek]

On Fri 2026-05-15 12:29:14, John Ogness wrote:
> On 2026-04-23, Petr Mladek <pmladek@suse.com> wrote:
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 13c98285892b..d251bf8e104f 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -2544,18 +2544,119 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
> >  }
> >  #endif
> >  
> > -static void set_user_specified(struct preferred_console *pc, bool user_specified)
> > +/** update_preferred_console - Update a given entry in the preferred_consoles[]
> > + *	table.
> 
> Perhaps the description should be:
> 
> Update or add a given entry in the preferred_consoles[] table.
> 
> If the caller didn't match an existing preferred_console, this function
> is called to add a new entry. This is obvious if you are looking at the
> caller, but it is not obvious at all if you are only looking at this
> function, i.e. strscpy'ing in @name or @devname is the only clue that
> you are dealing with a new entry.

Good point! I'll update the comment in v3. Also I'll rename the function to
add_or_update_preferred_console(). It is long but the function is
used only once so it does not harm that much ;-)

> > + * @i: index of the entry in @preferred_consoles table which should get updated.
> > + * @name: The name of the preferred console driver.
> > + * @idx: Preferred console index, e.g. port number.
> > + * @devname: The name of the preferred physical device.
> > + * @options: Options used when setting up the console driver.
> > + * @brl_options: Options used when setting up the console driver
> > + *	as a braille console.
> > + * @user_specified: True if preferred via the kernel command line.
> > + *
> > + * The function ensures that the given values are consistent. Also
> > + * it updates some global variables which are used to make the right
> > + * decisions in register_console().
> > + *
> > + * Rules:
> > + *
> > + *   1. Either @name and valid @idx OR @devname and @idx=-1 are allowed.
> > + *	Note that a valid @name and @idx will get assigned later when
> > + *	@devname matches during the device initialization.
> > + *   2. Specify @brl_options if the console should be enabled as
> > + *	a Braille console [*]
> > + *   3. Only matching entries can be updated.
> > + *   4. @options passed via the command line are used when the same
> > + *	console is preferred also by some platform-specific code.
> > + *
> > + * [*] Braille console is using the mechanism for registering consoles
> > + *     but it is very special. It is primarily used for user interaction
> > + *     with the system. It neither gets printk() messages nor is associated
> > + *     with /dev/console.
> > + */
> > +static int update_preferred_console(unsigned int i,
> > +				    const char *name, const short idx,
> > +				    const char *devname, char *options,
> > +				    char *brl_options, bool user_specified)
> >  {
> > -	if (!user_specified)
> > -		return;
> > +	struct preferred_console *pc;
> > +
> > +	if (i >= MAX_PREFERRED_CONSOLES)
> > +		return -E2BIG;
> > +
> > +	pc = &preferred_consoles[i];
> > +
> > +	if (!name && !devname)
> > +		return -EINVAL;
> 
> You are adding detailed error messages for all possible wrong calls
> except for this on. Maybe this should be covered as well with:
> 
> 	if (WARN_ON(!name && !devname))
> 		return -EINVAL;

Makes sense.

Also I am going print an error when reached the maximal number of
preferred consoles in the above check. It would look like:

	if (i >= MAX_PREFERRED_CONSOLES) {
		pr_err_once("Reached maximal number of preferred consoles.\n");
		return -E2BIG;
	}

It would be nice to print some more details. But it is not that easy
because we do not know whether "name" or "devname" is defined, ...
IMHO, it is not worth the complexity. I guess not nobody has reached
the limit in a real life scenario yet.

Best Regards,
Petr

[PATCH v2 4/9] printk: Cleanup _braille_(un)register_console() wrappers

[Petr Mladek]

The _braille_(un)register_console() wrappers currently attempt to hide
implementation details like the CON_BRL flag and pc->brl_options. This
forces callers to handle an unconventional tri-state return value (0 for
NOP, >0 for success, <0 for error), which makes the control flow harder
to follow and non-standard.

Refactor the wrappers to use standard kernel return codes (0 for success,
-ERRCODE on failure). Move the responsibility of checking brl_options
to the caller to make the logic more explicit.

Additionally, move the assignment of the CON_BRL flag from the internal
wrapper to braille_register_console(). This aligns it with how
CON_ENABLED is handled. To maintain symmetry and fix a potential bug
where flags might persist after removal, explicitly clear both
CON_ENABLED and CON_BRL in braille_unregister_console().

The patch should not change the existing behavior.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Marcos Paulo de Souza <mpdesouza@suse.com>
---
 drivers/accessibility/braille/braille_console.c |  7 ++++---
 kernel/printk/braille.c                         | 16 +++-------------
 kernel/printk/braille.h                         | 12 ++++++++++++
 kernel/printk/printk.c                          | 13 +++++--------
 4 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/drivers/accessibility/braille/braille_console.c b/drivers/accessibility/braille/braille_console.c
index 06b43b678d6e..7b324329882f 100644
--- a/drivers/accessibility/braille/braille_console.c
+++ b/drivers/accessibility/braille/braille_console.c
@@ -360,12 +360,12 @@ int braille_register_console(struct console *console, int index,
 		if (ret != 0)
 			return ret;
 	}
-	console->flags |= CON_ENABLED;
+	console->flags |= CON_ENABLED | CON_BRL;
 	console->index = index;
 	braille_co = console;
 	register_keyboard_notifier(&keyboard_notifier_block);
 	register_vt_notifier(&vt_notifier_block);
-	return 1;
+	return 0;
 }
 
 int braille_unregister_console(struct console *console)
@@ -375,5 +375,6 @@ int braille_unregister_console(struct console *console)
 	unregister_keyboard_notifier(&keyboard_notifier_block);
 	unregister_vt_notifier(&vt_notifier_block);
 	braille_co = NULL;
-	return 1;
+	console->flags &= ~(CON_ENABLED | CON_BRL);
+	return 0;
 }
diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
index 9d21a2bb1d38..593f83eb0487 100644
--- a/kernel/printk/braille.c
+++ b/kernel/printk/braille.c
@@ -37,22 +37,12 @@ int _braille_console_setup(char **str, char **brl_options)
 int
 _braille_register_console(struct console *console, struct preferred_console *pc)
 {
-	int rtn = 0;
-
-	if (pc->brl_options) {
-		console->flags |= CON_BRL;
-		rtn = braille_register_console(console, pc->index, pc->options,
-					       pc->brl_options);
-	}
-
-	return rtn;
+	return braille_register_console(console, pc->index, pc->options,
+					pc->brl_options);
 }
 
 int
 _braille_unregister_console(struct console *console)
 {
-	if (console->flags & CON_BRL)
-		return braille_unregister_console(console);
-
-	return 0;
+	return braille_unregister_console(console);
 }
diff --git a/kernel/printk/braille.h b/kernel/printk/braille.h
index 0bdac303f8b1..ec5feac1f508 100644
--- a/kernel/printk/braille.h
+++ b/kernel/printk/braille.h
@@ -11,6 +11,12 @@ braille_update_options(struct preferred_console *pc, char *brl_options)
 		pc->brl_options = brl_options;
 }
 
+static inline bool
+is_braille_console_preferred(struct preferred_console *pc)
+{
+	return (!!pc->brl_options);
+}
+
 /*
  * Setup console according to braille options.
  * Return -EINVAL on syntax error, 0 on success (or no braille option was
@@ -34,6 +40,12 @@ braille_update_options(struct preferred_console *pc, char *brl_options)
 {
 }
 
+static inline bool
+is_braille_console_preferred(struct preferred_console *pc)
+{
+	return false;
+}
+
 static inline int
 _braille_console_setup(char **str, char **brl_options)
 {
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index d251bf8e104f..7a3bbb0cb794 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -4001,8 +4001,8 @@ static int try_enable_preferred_console(struct console *newcon,
 			if (newcon->index < 0)
 				newcon->index = pc->index;
 
-			if (_braille_register_console(newcon, pc))
-				return 0;
+			if (is_braille_console_preferred(pc))
+				return _braille_register_console(newcon, pc);
 
 			err = console_call_setup(newcon, pc->options);
 			if (err)
@@ -4314,17 +4314,14 @@ static int unregister_console_locked(struct console *console)
 	bool found_boot_con = false;
 	unsigned long flags;
 	struct console *c;
-	int res;
+	int res = 0;
 
 	lockdep_assert_console_list_lock_held();
 
 	con_printk(KERN_INFO, console, "disabled\n");
 
-	res = _braille_unregister_console(console);
-	if (res < 0)
-		return res;
-	if (res > 0)
-		return 0;
+	if (console->flags & CON_BRL)
+		return _braille_unregister_console(console);
 
 	if (!console_is_registered_locked(console))
 		res = -ENODEV;
-- 
2.53.0

Re: [PATCH v2 4/9] printk: Cleanup _braille_(un)register_console() wrappers

[John Ogness]

On 2026-04-23, Sashiko wrote:
>> diff --git a/drivers/accessibility/braille/braille_console.c b/drivers/accessibility/braille/braille_console.c
>> index 06b43b678d6e..7b324329882f 100644
>> --- a/drivers/accessibility/braille/braille_console.c
>> +++ b/drivers/accessibility/braille/braille_console.c
>> @@ -360,12 +360,12 @@ int braille_register_console(struct console *console, int index,
>>  		if (ret != 0)
>>  			return ret;
>>  	}
>> -	console->flags |= CON_ENABLED;
>> +	console->flags |= CON_ENABLED | CON_BRL;
>>  	console->index = index;
>>  	braille_co = console;
>>  	register_keyboard_notifier(&keyboard_notifier_block);
>>  	register_vt_notifier(&vt_notifier_block);
>> -	return 1;
>> +	return 0;
>>  }
>
> While reviewing this function, I noticed a pre-existing
> regression. The printk subsystem relies on console_lock() to serialize
> console setup against boot consoles that might be actively printing to
> the same hardware port.  For normal consoles, this synchronization is
> handled explicitly:
>
> kernel/printk/printk.c:console_call_setup() {
>     ...
>     console_lock();
>     err = newcon->setup(newcon, options);
>     console_unlock();
>     ...
> }
>
> However, it looks like braille_register_console() bypasses this
> protection and directly invokes console->setup() just above this block
> without acquiring console_lock().
>
> Could this unprotected setup call cause a data race or hardware state
> corruption if the underlying driver shares the hardware with an active
> boot console?

I do not know enough about braille consoles if they can also be early
consoles, but it makes sense to synchronize the ->setup()
callback. Something like this:

--- a/drivers/accessibility/braille/braille_console.c
+++ b/drivers/accessibility/braille/braille_console.c
@@ -356,7 +356,9 @@ int braille_register_console(struct console *console, int index,
 	if (braille_co)
 		return -ENODEV;
 	if (console->setup) {
+		console_lock();
 		ret = console->setup(console, console_options);
+		console_unlock();
 		if (ret != 0)
 			return ret;
 	}

>>  int braille_unregister_console(struct console *console)
>> @@ -375,5 +375,6 @@ int braille_unregister_console(struct console *console)
>>  	unregister_keyboard_notifier(&keyboard_notifier_block);
>>  	unregister_vt_notifier(&vt_notifier_block);
>>  	braille_co = NULL;
>> -	return 1;
>> +	console->flags &= ~(CON_ENABLED | CON_BRL);
>> +	return 0;
>>  }
>
> This also appears to be a pre-existing regression. The
> unregister_keyboard_notifier() and unregister_vt_notifier() functions
> remove callbacks from atomic notifier chains. Since atomic notifiers
> execute their callbacks under RCU read lock, unregistering them only
> unlinks the node without blocking for concurrent callbacks to finish.
>
> By immediately clearing the global braille_co pointer and returning,
> could a concurrently executing keyboard_notifier_call that already
> passed the braille_co check on another CPU cause a use-after-free or
> null pointer dereference?
>
> Does this function need a synchronize_rcu() before returning to ensure
> all callbacks have completed?

atomic_notifier_chain_unregister() already calls synchronize_rcu()
before returning, so no action is needed here.

For this patch as it is:

Reviewed-by: John Ogness <john.ogness@linutronix.de>

(The console lock/unlock should be a separate patch.)

John

[PATCH v2 5/9] printk: Separate code for enabling console

[Petr Mladek]

There are several code paths which try to enable a newly registered
console. Move the logic into a separate try_enable_console() function.

It simplifies a bit the long register_console() function definition.

Also followup patches are going to add even more code paths. And it will
be easier to use "return" when it does not make sense to try other
variants.

The patch does not change the existing behavior.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 64 ++++++++++++++++++++++++------------------
 1 file changed, 36 insertions(+), 28 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7a3bbb0cb794..2543c810efcb 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -4040,6 +4040,41 @@ static void try_enable_default_console(struct console *newcon)
 		newcon->flags |= CON_CONSDEV;
 }
 
+#define console_first()				\
+	hlist_entry(console_list.first, struct console, node)
+
+static int try_enable_console(struct console *newcon)
+{
+	int err;
+
+	/*
+	 * See if we want to enable this console driver by default.
+	 *
+	 * Nope when a console is preferred by the command line, device
+	 * tree, or SPCR.
+	 *
+	 * The first real console with tty binding (driver) wins. More
+	 * consoles might get enabled before the right one is found.
+	 *
+	 * Note that a console with tty binding will have CON_CONSDEV
+	 * flag set and will be first in the list.
+	 */
+	if (preferred_dev_console < 0) {
+		if (hlist_empty(&console_list) || !console_first()->device ||
+		    console_first()->flags & CON_BOOT) {
+			try_enable_default_console(newcon);
+		}
+	}
+
+	/* See if this console matches one we selected on the command line */
+	err = try_enable_preferred_console(newcon, true);
+	if (err != -ENOENT)
+		return err;
+
+	/* If not, try to match against the platform default(s) */
+	return try_enable_preferred_console(newcon, false);
+}
+
 /* Return the starting sequence number for a newly registered console. */
 static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered)
 {
@@ -4114,9 +4149,6 @@ static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered)
 	return init_seq;
 }
 
-#define console_first()				\
-	hlist_entry(console_list.first, struct console, node)
-
 static int unregister_console_locked(struct console *console);
 
 /*
@@ -4178,31 +4210,7 @@ void register_console(struct console *newcon)
 			goto unlock;
 	}
 
-	/*
-	 * See if we want to enable this console driver by default.
-	 *
-	 * Nope when a console is preferred by the command line, device
-	 * tree, or SPCR.
-	 *
-	 * The first real console with tty binding (driver) wins. More
-	 * consoles might get enabled before the right one is found.
-	 *
-	 * Note that a console with tty binding will have CON_CONSDEV
-	 * flag set and will be first in the list.
-	 */
-	if (preferred_dev_console < 0) {
-		if (hlist_empty(&console_list) || !console_first()->device ||
-		    console_first()->flags & CON_BOOT) {
-			try_enable_default_console(newcon);
-		}
-	}
-
-	/* See if this console matches one we selected on the command line */
-	err = try_enable_preferred_console(newcon, true);
-
-	/* If not, try to match against the platform default(s) */
-	if (err == -ENOENT)
-		err = try_enable_preferred_console(newcon, false);
+	err = try_enable_console(newcon);
 
 	/* printk() messages are not printed to the Braille console. */
 	if (err || newcon->flags & CON_BRL) {
-- 
2.53.0

Re: [PATCH v2 5/9] printk: Separate code for enabling console

[Marcos Paulo de Souza]

On Thu, 2026-04-23 at 15:00 +0200, Petr Mladek wrote:
> There are several code paths which try to enable a newly registered
> console. Move the logic into a separate try_enable_console()
> function.
> 
> It simplifies a bit the long register_console() function definition.
> 
> Also followup patches are going to add even more code paths. And it
> will
> be easier to use "return" when it does not make sense to try other
> variants.
> 
> The patch does not change the existing behavior.
> 
> Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Marcos Paulo de Souza <mpdesouza@suse.com>

> ---
>  kernel/printk/printk.c | 64 ++++++++++++++++++++++++----------------
> --
>  1 file changed, 36 insertions(+), 28 deletions(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 7a3bbb0cb794..2543c810efcb 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -4040,6 +4040,41 @@ static void try_enable_default_console(struct
> console *newcon)
>  		newcon->flags |= CON_CONSDEV;
>  }
>  
> +#define console_first()				\
> +	hlist_entry(console_list.first, struct console, node)
> +
> +static int try_enable_console(struct console *newcon)
> +{
> +	int err;
> +
> +	/*
> +	 * See if we want to enable this console driver by default.
> +	 *
> +	 * Nope when a console is preferred by the command line,
> device
> +	 * tree, or SPCR.
> +	 *
> +	 * The first real console with tty binding (driver) wins.
> More
> +	 * consoles might get enabled before the right one is found.
> +	 *
> +	 * Note that a console with tty binding will have
> CON_CONSDEV
> +	 * flag set and will be first in the list.
> +	 */
> +	if (preferred_dev_console < 0) {
> +		if (hlist_empty(&console_list) || !console_first()-
> >device ||
> +		    console_first()->flags & CON_BOOT) {
> +			try_enable_default_console(newcon);
> +		}
> +	}
> +
> +	/* See if this console matches one we selected on the
> command line */
> +	err = try_enable_preferred_console(newcon, true);
> +	if (err != -ENOENT)
> +		return err;
> +
> +	/* If not, try to match against the platform default(s) */
> +	return try_enable_preferred_console(newcon, false);
> +}
> +
>  /* Return the starting sequence number for a newly registered
> console. */
>  static u64 get_init_console_seq(struct console *newcon, bool
> bootcon_registered)
>  {
> @@ -4114,9 +4149,6 @@ static u64 get_init_console_seq(struct console
> *newcon, bool bootcon_registered)
>  	return init_seq;
>  }
>  
> -#define console_first()				\
> -	hlist_entry(console_list.first, struct console, node)
> -
>  static int unregister_console_locked(struct console *console);
>  
>  /*
> @@ -4178,31 +4210,7 @@ void register_console(struct console *newcon)
>  			goto unlock;
>  	}
>  
> -	/*
> -	 * See if we want to enable this console driver by default.
> -	 *
> -	 * Nope when a console is preferred by the command line,
> device
> -	 * tree, or SPCR.
> -	 *
> -	 * The first real console with tty binding (driver) wins.
> More
> -	 * consoles might get enabled before the right one is found.
> -	 *
> -	 * Note that a console with tty binding will have
> CON_CONSDEV
> -	 * flag set and will be first in the list.
> -	 */
> -	if (preferred_dev_console < 0) {
> -		if (hlist_empty(&console_list) || !console_first()-
> >device ||
> -		    console_first()->flags & CON_BOOT) {
> -			try_enable_default_console(newcon);
> -		}
> -	}
> -
> -	/* See if this console matches one we selected on the
> command line */
> -	err = try_enable_preferred_console(newcon, true);
> -
> -	/* If not, try to match against the platform default(s) */
> -	if (err == -ENOENT)
> -		err = try_enable_preferred_console(newcon, false);
> +	err = try_enable_console(newcon);
>  
>  	/* printk() messages are not printed to the Braille console.
> */
>  	if (err || newcon->flags & CON_BRL) {

Re: [PATCH v2 5/9] printk: Separate code for enabling console

[John Ogness]

On 2026-04-23, Petr Mladek <pmladek@suse.com> wrote:
> There are several code paths which try to enable a newly registered
> console. Move the logic into a separate try_enable_console() function.
>
> It simplifies a bit the long register_console() function definition.
>
> Also followup patches are going to add even more code paths. And it will
> be easier to use "return" when it does not make sense to try other
> variants.
>
> The patch does not change the existing behavior.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>

Reviewed-by: John Ogness <john.ogness@linutronix.de>

[PATCH v2 6/9] printk: Try to register each console as Braille first

[Petr Mladek]

Braille consoles are unique: they can only be enabled via the command
line and use the preferred console framework for initialization, yet
they are never added to the console_list or associated with
/dev/console. Because of this, the preferred_console variable remains
unset when only a Braille console is requested.

Currently, try_enable_preferred_console() must be called even when
"preferred_dev_console" variable is not set, just to catch these "hidden"
Braille requests.

Refactor the logic by adding a parameter to try_enable_preferred_console()
to explicitly handle Braille vs. non-Braille cases. It will eventually
allow to skip try_enable_preferred_console() when there are no preferred
consoles. This improves code robustness by ensuring the console
setup is explicit and only performed once.

Note that _braille_register_console() is skipped when the given console
driver has a match() callback and it succeeded. It means that it took
over an early console and can't be used as a Braille console.

As a result try_enable_braille_console() might return success even
when it did not enabled the console in the Braille mode. It is
the reason why register_console() has to explicitly check whether
CON_BRL flag was really set and could skip the further steps.

The refactoring even fixes two subtle bugs:

1. When only the Braille console is defined on the command line,
   the original code might attempt to enable the same console twice—once
   as a default and once as a Braille console. This results in calling
   the setup() callback twice and incorrectly setting the CON_CONSDEV flag.

2. When the same console is defined on the command line using devname
   and then as Braille console, for example:

      console=00:00:0.0,115200 console=brl,ttyS0,115200

   It would have two separate entries in preferred_consoles[] array.

   The 2nd (Braille) entry would be used when univ8250_console_init()
   tries to register the generic "ttyS" console driver. Note that
   the 1st entry still does not have defined the "name" entry at
   this stage.

   The 1st non-Braille entry would be used later when serial8250_init()
   registers all found devices, assigns "tty0" for the given "00:00:0.0"
   devname and tries to register the same struct console once again.

   The original code would call newcon->setup() twice in this scenario.
   It won't add the console into console_list only because the later
   check in register_console() would detect CON_BRL flag set from
   the 1st registration and return early.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 56 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 50 insertions(+), 6 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2543c810efcb..e34955189d16 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -367,6 +367,7 @@ static int console_locked;
 static struct preferred_console preferred_consoles[MAX_PREFERRED_CONSOLES];
 
 static int preferred_dev_console = -1;
+static bool want_braille_console;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
@@ -2644,7 +2645,9 @@ static int update_preferred_console(unsigned int i,
 
 	braille_update_options(pc, brl_options);
 
-	if (!brl_options)
+	if (brl_options)
+		want_braille_console = true;
+	else
 		preferred_dev_console = i;
 
 	/*
@@ -3975,8 +3978,9 @@ static int console_call_setup(struct console *newcon, char *options)
  * Care need to be taken with consoles that are statically
  * enabled such as netconsole
  */
-static int try_enable_preferred_console(struct console *newcon,
-					bool user_specified)
+static int __try_enable_preferred_console(struct console *newcon,
+					  bool user_specified,
+					  bool try_only_braille)
 {
 	struct preferred_console *pc;
 	int i, err;
@@ -3987,8 +3991,19 @@ static int try_enable_preferred_console(struct console *newcon,
 		/* Console not yet initialized? */
 		if (!pc->name[0])
 			continue;
-		if (pc->user_specified != user_specified)
-			continue;
+
+		/*
+		 * @try_only_braille and @user_specifified define which
+		 * preferred console entries are handled in this round.
+		 */
+		if (try_only_braille) {
+			if (!is_braille_console_preferred(pc))
+				continue;
+		} else {
+			if (pc->user_specified != user_specified)
+				continue;
+		}
+
 		if (!newcon->match ||
 		    newcon->match(newcon, pc->name, pc->index, pc->options) != 0) {
 			/* default matching */
@@ -4001,7 +4016,7 @@ static int try_enable_preferred_console(struct console *newcon,
 			if (newcon->index < 0)
 				newcon->index = pc->index;
 
-			if (is_braille_console_preferred(pc))
+			if (try_only_braille)
 				return _braille_register_console(newcon, pc);
 
 			err = console_call_setup(newcon, pc->options);
@@ -4025,6 +4040,17 @@ static int try_enable_preferred_console(struct console *newcon,
 	return -ENOENT;
 }
 
+static int try_enable_preferred_console(struct console *newcon,
+					bool user_specified)
+{
+	return __try_enable_preferred_console(newcon, user_specified, false);
+}
+
+static int try_enable_braille_console(struct console *newcon)
+{
+	return __try_enable_preferred_console(newcon, true, true);
+}
+
 /* Try to enable the console unconditionally */
 static void try_enable_default_console(struct console *newcon)
 {
@@ -4047,6 +4073,24 @@ static int try_enable_console(struct console *newcon)
 {
 	int err;
 
+	/*
+	 * First, try to enable the console driver as a Braille console.
+	 * It would have metadata in the preferred_consoles[] array.
+	 * But it won't be counted as @preferred_console because
+	 * it does not get printk() messages and is not associated
+	 * with /dev/console.
+	 *
+	 * Note that it might succeed also when the driver has a match()
+	 * callback and it took over a boot console. In this case,
+	 * the driver will continue working as a classic non-Braille
+	 * console.
+	 */
+	if (want_braille_console) {
+		err = try_enable_braille_console(newcon);
+		if (err != -ENOENT)
+			return err;
+	}
+
 	/*
 	 * See if we want to enable this console driver by default.
 	 *
-- 
2.53.0

[PATCH v2 7/9] printk: Do not set Braille console as preferred_console

[Petr Mladek]

The Braille console reuses the framework for handling consoles preferred
via the command line. However, it is a special-purpose interface that
neither receives standard printk messages nor associates with
/dev/console.

Currently, the "preferred_dev_console" variable can point to a Braille
console entry in the "preferred_consoles[]" array. This occurs if an
entry was first created for a non-Braille console, but a later 'console='
parameter redefined it as a Braille console.

Since a Braille console will only ever be enabled as such, it should not
be tracked as the primary system console. Adjust the logic to ensure
"preferred_dev_console" continues to point to the previously designated
normal console instead.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e34955189d16..9143a050c289 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -367,6 +367,7 @@ static int console_locked;
 static struct preferred_console preferred_consoles[MAX_PREFERRED_CONSOLES];
 
 static int preferred_dev_console = -1;
+static int preferred_dev_console_prev = -1;
 static bool want_braille_console;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
@@ -2566,10 +2567,11 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
  *	Note that a valid @name and @idx will get assigned later when
  *	@devname matches during the device initialization.
  *   2. Specify @brl_options if the console should be enabled as
- *	a Braille console [*]
+ *	a Braille console.
  *   3. Only matching entries can be updated.
  *   4. @options passed via the command line are used when the same
  *	console is preferred also by some platform-specific code.
+ *   5. Braille console is never associated with /dev/console.[*]
  *
  * [*] Braille console is using the mechanism for registering consoles
  *     but it is very special. It is primarily used for user interaction
@@ -2645,10 +2647,22 @@ static int update_preferred_console(unsigned int i,
 
 	braille_update_options(pc, brl_options);
 
-	if (brl_options)
+	/*
+	 * The last preferred console should get associated with /dev/console.
+	 * Except for the Braille console which can't get associated with
+	 * /dev/console. One level history should be enough because only one,
+	 * the VisioBraille device, is supported at the moment.
+	 */
+	if (brl_options) {
 		want_braille_console = true;
-	else
+		if (preferred_dev_console == i) {
+			preferred_dev_console = preferred_dev_console_prev;
+			preferred_dev_console_prev = -1;
+		}
+	} else if (!is_braille_console_preferred(pc)) {
+		preferred_dev_console_prev = preferred_dev_console;
 		preferred_dev_console = i;
+	}
 
 	/*
 	 * @pc console was defined by the user on the command line.
-- 
2.53.0

[PATCH v2 8/9] printk: Handle pre-enabled consoles in the top-level try_enable_console()

[Petr Mladek]

The function try_enable_preferred_console() currently has the
non-obvious side effect of returning success for consoles that are
already pre-enabled. This obscures the logic flow during console
registration.

Move the check for pre-enabled consoles directly into the top-level
try_enable_console(). This change makes the handling of pre-enabled
consoles explicit and easier to follow.

Furthermore, this separation lays the groundwork for future cleanups
where try_enable_preferred_console() can be restricted to cases where
an entry actually exists in the preferred_consoles[] array.

Possible behavior change:

try_enable_preferred_console() will newly be called also with
@user_specified parameter set to "false" when it failed with the "true"
variant. But it looks like the right way to do. It will allow to call
newcon->setup() when the console was preferred by some platform
specific code.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9143a050c289..91c3be6843bc 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3988,9 +3988,6 @@ static int console_call_setup(struct console *newcon, char *options)
  * the newly registered console with any of the ones selected
  * by either the command line or add_preferred_console() and
  * setup/enable it.
- *
- * Care need to be taken with consoles that are statically
- * enabled such as netconsole
  */
 static int __try_enable_preferred_console(struct console *newcon,
 					  bool user_specified,
@@ -4043,14 +4040,6 @@ static int __try_enable_preferred_console(struct console *newcon,
 		return 0;
 	}
 
-	/*
-	 * Some consoles, such as pstore and netconsole, can be enabled even
-	 * without matching. Accept the pre-enabled consoles only when match()
-	 * and setup() had a chance to be called.
-	 */
-	if (newcon->flags & CON_ENABLED && pc->user_specified == user_specified)
-		return 0;
-
 	return -ENOENT;
 }
 
@@ -4130,7 +4119,19 @@ static int try_enable_console(struct console *newcon)
 		return err;
 
 	/* If not, try to match against the platform default(s) */
-	return try_enable_preferred_console(newcon, false);
+	err = try_enable_preferred_console(newcon, false);
+	if (err != -ENOENT)
+		return err;
+
+	/*
+	 * Some consoles, such as pstore and netconsole, can be enabled even
+	 * without matching. Accept them at this stage when they had a chance
+	 * to match() and call setup().
+	 */
+	if (newcon->flags & CON_ENABLED)
+		err = 0;
+
+	return err;
 }
 
 /* Return the starting sequence number for a newly registered console. */
-- 
2.53.0

[PATCH v2 9/9] printk: Try enable preferred consoles only when there are any

[Petr Mladek]

try_enable_preferred_console() used to be always called because it
had several hidden effects, namely:

- enabled Braille consoles which were ignored by "preferred_dev_console"
  because they were not associated with /dev/console.

- returned success when a console was pre-enabled using CON_ENABLED
  flag.

- returned success when a console was enabled by default because
  try_enable_default_console() did not return success.

The first two hidden effects were removed in previous patches. Remove
the last one so that try_enable_preferred_console() can be called only
when any non-Braille console is preferred.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 91c3be6843bc..4098ed3b735f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -4055,18 +4055,23 @@ static int try_enable_braille_console(struct console *newcon)
 }
 
 /* Try to enable the console unconditionally */
-static void try_enable_default_console(struct console *newcon)
+static int try_enable_default_console(struct console *newcon)
 {
+	int err;
+
 	if (newcon->index < 0)
 		newcon->index = 0;
 
-	if (console_call_setup(newcon, NULL) != 0)
-		return;
+	err = console_call_setup(newcon, NULL);
+	if (err)
+		return err;
 
 	newcon->flags |= CON_ENABLED;
 
 	if (newcon->device)
 		newcon->flags |= CON_CONSDEV;
+
+	return 0;
 }
 
 #define console_first()				\
@@ -4109,7 +4114,9 @@ static int try_enable_console(struct console *newcon)
 	if (preferred_dev_console < 0) {
 		if (hlist_empty(&console_list) || !console_first()->device ||
 		    console_first()->flags & CON_BOOT) {
-			try_enable_default_console(newcon);
+			err = try_enable_default_console(newcon);
+			if (err != -ENOENT)
+				return err;
 		}
 	}
 
-- 
2.53.0

Re: [PATCH v2 9/9] printk: Try enable preferred consoles only when there are any

[Petr Mladek]

On Thu 2026-04-23 15:00:14, Petr Mladek wrote:
> try_enable_preferred_console() used to be always called because it
> had several hidden effects, namely:
> 
> - enabled Braille consoles which were ignored by "preferred_dev_console"
>   because they were not associated with /dev/console.
> 
> - returned success when a console was pre-enabled using CON_ENABLED
>   flag.
> 
> - returned success when a console was enabled by default because
>   try_enable_default_console() did not return success.
> 
> The first two hidden effects were removed in previous patches. Remove
> the last one so that try_enable_preferred_console() can be called only
> when any non-Braille console is preferred.
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -4055,18 +4055,23 @@ static int try_enable_braille_console(struct console *newcon)
>  }
>  
>  /* Try to enable the console unconditionally */
> -static void try_enable_default_console(struct console *newcon)
> +static int try_enable_default_console(struct console *newcon)
>  {
> +	int err;
> +
>  	if (newcon->index < 0)
>  		newcon->index = 0;
>  
> -	if (console_call_setup(newcon, NULL) != 0)
> -		return;
> +	err = console_call_setup(newcon, NULL);
> +	if (err)
> +		return err;
>  
>  	newcon->flags |= CON_ENABLED;
>  
>  	if (newcon->device)
>  		newcon->flags |= CON_CONSDEV;
> +
> +	return 0;
>  }
>  
>  #define console_first()				\
> @@ -4109,7 +4114,9 @@ static int try_enable_console(struct console *newcon)
>  	if (preferred_dev_console < 0) {
>  		if (hlist_empty(&console_list) || !console_first()->device ||
>  		    console_first()->flags & CON_BOOT) {
> -			try_enable_default_console(newcon);
> +			err = try_enable_default_console(newcon);
> +			if (err != -ENOENT)
> +				return err;
>  		}
>  	}

I am working on v3 and I realized that this is not enough.
try_enable_preferred_console() is still called when
there already was default console (the if-condition above failed).
But it makes sense only when preferred_dev_console >= 0.

I am going to go further and put it into "else" part.
I'll actually invert the check and do:

static int try_enable_console(struct console *newcon)
{
	int err;

	/*
	 * First, try to enable the console driver as a Braille console.
	 * It would have metadata in the preferred_consoles[] array.
	 * But it won't be counted as @preferred_console because
	 * it does not get printk() messages and is not associated
	 * with /dev/console.
	 *
	 * Note that it might succeed also when the driver has a match()
	 * callback and it took over a boot console. In this case,
	 * the driver will continue working as a classic non-Braille
	 * console.
	 */
	if (want_braille_console) {
		err = try_enable_braille_console(newcon);
		if (err != -ENOENT)
			return err;
	}

	if (preferred_dev_console >= 0) {
		/* See if this console matches one we selected on the command line */
		err = try_enable_preferred_console(newcon, true);
		if (err != -ENOENT)
			return err;

		/* If not, try to match against the platform default(s) */
		err = try_enable_preferred_console(newcon, false);
		if (err != -ENOENT)
			return err;
	} else {
		/*
		 * See if we want to enable this console driver by default.
		 *
		 * Nope when a console is preferred by the command line, device
		 * tree, or SPCR.
		 *
		 * The first real console with tty binding (driver) wins. More
		 * consoles might get enabled before the right one is found.
		 *
		 * Note that a console with tty binding will have CON_CONSDEV
		 * flag set and will be first in the list.
		 */
		if (hlist_empty(&console_list) || !console_first()->device ||
		    console_first()->flags & CON_BOOT) {
			err = try_enable_default_console(newcon);
			if (err != -ENOENT)
				return err;
		}
	}

	/*
	 * Some consoles, such as pstore and netconsole, can be enabled even
	 * without matching. Accept them at this stage when they had a chance
	 * to match() and call setup().
	 */
	if (newcon->flags & CON_ENABLED)
		err = 0;

	return err;
}

I am going to split this into two patches:

   1. Invert the logic and add the "else" part. This should
      not change the behavior at this stage.

   2. Add the return value for try_enabled_default_console()
      and return immediately on success or error. It might
      actually change the behavior because pre-enabled
      console won't be registered when newcon->setup()
      failed.

Best Regards,
Petr

Re: [PATCH v2 0/9] printk: Clean up preferred console handling

[Petr Mladek]

On Thu 2026-04-23 15:00:05, Petr Mladek wrote:
> Hi,
> 
> this patchset does some clean up of the code for handling preferred consoles
> in the console registration code.

JFYI, Sashiko AI has already proceed this patchset and reported some
interesting problems. [1] I still have to think about it.

Anyway, you do not need to report the issues already reported
by Sashiko AI. I am going to process them. But feel free
to comment on them especially when the opinion is not obvious ;-)

[1] https://sashiko.dev/#/patchset/20260423130015.85175-1-pmladek%40suse.com

Best Regards,
Petr