[PATCH v6 1/6] printk: Save console options for add_preferred_console_match()

Tony Lindgren
2024-02-13T08:47:04Z

Driver subsystems may need to translate the preferred console name to the
character device name used. We already do some of this in console_setup()
with a few hardcoded names, but that does not scale well.

The console options are parsed early in console_setup(), and the consoles
are added with __add_preferred_console(). At this point we don't know much
about the character device names and device drivers getting probed.

To allow driver subsystems to set up a preferred console, let's save the
kernel command line console options. To add a preferred console from a
driver subsystem with optional character device name translation, let's
add a new function add_preferred_console_match().

This allows the serial core layer to support console=DEVNAME:0.0 style
hardware based addressing in addition to the current console=ttyS0 style
naming. And we can start moving console_setup() character device parsing
to the driver subsystem specific code.

We use a separate array from the console_cmdline array as the character
device name and index may be unknown at the console_setup() time. And
eventually there's no need to call __add_preferred_console() until the
subsystem is ready to handle the console.

Adding the console name in addition to the character device name, and a
flag for an added console, could be added to the struct console_cmdline.
And the console_cmdline array handling could be modified accordingly. But
that complicates things compared saving the console options, and then
adding the consoles when the subsystems handling the consoles are ready.

Signed-off-by: Tony Lindgren <tony@atomide.com>
---
include/linux/printk.h | 3 +
kernel/printk/Makefile | 2 +-
kernel/printk/conopt.c | 143 ++++++++++++++++++++++++++++++++
kernel/printk/console_cmdline.h | 6 ++
kernel/printk/printk.c | 14 +++-
5 files changed, 164 insertions(+), 4 deletions(-)
create mode 100644 kernel/printk/conopt.c

diff --git a/include/linux/printk.h b/include/linux/printk.h
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -60,6 +60,9 @@ static inline const char *printk_skip_headers(const char *buffer)
#define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT
#define CONSOLE_LOGLEVEL_QUIET CONFIG_CONSOLE_LOGLEVEL_QUIET

+int add_preferred_console_match(const char *match, const char *name,
+ const short idx);
+
extern int console_printk[];

#define console_loglevel (console_printk[0])
diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile
--- a/kernel/printk/Makefile
+++ b/kernel/printk/Makefile
@@ -1,5 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
-obj-y = printk.o
+obj-y = printk.o conopt.o
obj-$(CONFIG_PRINTK) += printk_safe.o nbcon.o
obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o
obj-$(CONFIG_PRINTK_INDEX) += index.o
diff --git a/kernel/printk/conopt.c b/kernel/printk/conopt.c
new file mode 100644
--- /dev/null
+++ b/kernel/printk/conopt.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kernel command line console options for hardware based addressing
+ *
+ * Copyright (C) 2023 Texas Instruments Incorporated - https://www.ti.com/
+ * Author: Tony Lindgren <tony@atomide.com>
+ */
+
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include <asm/errno.h>
+
+#include "console_cmdline.h"
+
+/*
+ * Allow longer DEVNAME:0.0 style console naming such as abcd0000.serial:0.0
+ * in addition to the legacy ttyS0 style naming.
+ */
+#define CONSOLE_NAME_MAX 32
+
+#define CONSOLE_OPT_MAX 16
+#define CONSOLE_BRL_OPT_MAX 16
+
+struct console_option {
+ char name[CONSOLE_NAME_MAX];
+ char opt[CONSOLE_OPT_MAX];
+ char brl_opt[CONSOLE_BRL_OPT_MAX];
+ u8 has_brl_opt:1;
+};
+
+/* Updated only at console_setup() time, no locking needed */
+static struct console_option conopt[MAX_CMDLINECONSOLES];
+
+/**
+ * console_opt_save - Saves kernel command line console option for driver use
+ * @str: Kernel command line console name and option
+ * @brl_opt: Braille console options
+ *
+ * Saves a kernel command line console option for driver subsystems to use for
+ * adding a preferred console during init. Called from console_setup() only.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int __init console_opt_save(const char *str, const char *brl_opt)
+{
+ struct console_option *con;
+ const char *opt = NULL;
+ size_t namelen, optlen;
+ int i;
+
+ namelen = strcspn(str, ",");
+ if (!namelen)
+ return -EINVAL;
+
+ optlen = strlen(str) - namelen;
+ if (optlen > 1)
+ opt = str + namelen + 1;
+
+ if (namelen >= CONSOLE_NAME_MAX || optlen >= CONSOLE_OPT_MAX)
+ return -EINVAL;
+
+ for (i = 0; i < MAX_CMDLINECONSOLES; i++) {
+ con = &conopt[i];
+
+ if (con->name[0]) {
+ if (!strncmp(str, con->name, namelen))
+ return 0;
+ continue;
+ }
+
+ strscpy(con->name, str, namelen + 1);
+ if (opt)
+ strscpy(con->opt, opt, optlen + 1);
+
+ /* See _braille_console_setup(), both empty and NULL are valid */
+ if (brl_opt) {
+ strscpy(con->brl_opt, brl_opt, CONSOLE_BRL_OPT_MAX);
+ con->has_brl_opt = 1;
+ }
+
+ return 0;
+ }
+
+ return -ENOMEM;
+}
+
+static struct console_option *console_opt_find(const char *name)
+{
+ struct console_option *con;
+ int i;
+
+ for (i = 0; i < MAX_CMDLINECONSOLES; i++) {
+ con = &conopt[i];
+ if (!strcmp(name, con->name))
+ return con;
+ }
+
+ return NULL;
+}
+
+/**
+ * add_preferred_console_match - Adds a preferred console if a match is found
+ * @match: Expected console on kernel command line, such as console=DEVNAME:0.0
+ * @name: Name of the console character device to add such as ttyS
+ * @idx: Index for the console
+ *
+ * Allows driver subsystems to add a console after translating the command
+ * line name to the character device name used for the console. Options are
+ * added automatically based on the kernel command line. Duplicate preferred
+ * consoles are ignored by __add_preferred_console().
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int add_preferred_console_match(const char *match, const char *name,
+ const short idx)
+{
+ struct console_option *con;
+ char *brl_opt = NULL;
+
+ if (!match || !strlen(match) || !name || !strlen(name) ||
+ idx < 0)
+ return -EINVAL;
+
+ con = console_opt_find(match);
+ if (!con)
+ return -ENOENT;
+
+ /*
+ * See __add_preferred_console(). It checks for NULL brl_options to set
+ * the preferred_console flag. Empty brl_opt instead of NULL leads into
+ * the preferred_console flag not set, and CON_CONSDEV not being set,
+ * and the boot console won't get disabled at the end of console_setup().
+ */
+ if (con->has_brl_opt)
+ brl_opt = con->brl_opt;
+
+ console_opt_add_preferred_console(name, idx, con->opt, brl_opt);
+
+ return 0;
+}
diff --git a/kernel/printk/console_cmdline.h b/kernel/printk/console_cmdline.h
--- a/kernel/printk/console_cmdline.h
+++ b/kernel/printk/console_cmdline.h
@@ -2,6 +2,12 @@
#ifndef _CONSOLE_CMDLINE_H
#define _CONSOLE_CMDLINE_H

+#define MAX_CMDLINECONSOLES 8
+
+int console_opt_save(const char *str, const char *brl_opt);
+int console_opt_add_preferred_console(const char *name, const short idx,
+ char *options, char *brl_options);
+
struct console_cmdline
{
char name[16]; /* Name of the driver */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -360,9 +360,6 @@ static int console_locked;
/*
* Array of consoles built from command line options (console=)
*/
-
-#define MAX_CMDLINECONSOLES 8
-
static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];

static int preferred_console = -1;
@@ -2458,6 +2455,10 @@ static int __init console_setup(char *str)
if (_braille_console_setup(&str, &brl_options))
return 1;

+ /* Save the console for driver subsystem use */
+ if (console_opt_save(str, brl_options))
+ return 1;
+
/*
* Decode str into name, index, options.
*/
@@ -2488,6 +2489,13 @@ static int __init console_setup(char *str)
}
__setup("console=", console_setup);

+/* Only called from add_preferred_console_match() */
+int console_opt_add_preferred_console(const char *name, const short idx,
+ char *options, char *brl_options)
+{
+ return __add_preferred_console(name, idx, options, brl_options, true);
+}
+
/**
* add_preferred_console - add a device to the list of preferred consoles.
* @name: device name
--
2.43.1