Re: [PATCH v3 -next 11/11] serial: 8250_early: Remove setup_early_serial8250_console()

Yinghai Lu
2015-04-02T09:15:29Z

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On Wed, Apr 1, 2015 at 8:22 PM, Peter Hurley <peter@hurleysoftware.com> wrote:
> The documented behavior of console=ttyS options, to which your
> quote refers, clearly states:
>
> Default is "9600n8".

drivers/tty/serial/8250/8250_early.c:early_serial8250_setup
still have calling to probe_baud, but it is not triggered.

Here is root cause.
The gap between entries in earlycon_table cause
iteration fail to find next entry, so uart8250 handler is
not called proplerly.

attached patch fix the problem.

Thanks

Yinghai

[-- Attachment #2: fix_earlycon_alignment.patch --]
[-- Type: text/x-patch, Size: 4743 bytes --]

Subject: [PATCH] serial: Fix earlycon section iteration

Found when booting with console=uart8250,io,0x3f8
the kernel will revert baud rate to 9600 instead of keeping 115200.

root causes: The gap between entries in earlycon_table cause
iteration fail to find next entry, so uart8250 handler is
not called proplerly.

commit d2fd6810a823 ("tty/serial: convert 8250 to generic earlycon")
add two entries into earlycon_table.
EARLYCON_DECLARE(uart8250, early_serial8250_setup);
EARLYCON_DECLARE(uart, early_serial8250_setup);

and according to System.map, earlycon_uart is before earlycon_uart8250.
ffffffff832049a0 t __earlycon_uart
ffffffff832049c0 t __earlycon_uart8250
And offset between two entries is 0x20.

commit 470ca0de69fe ("serial: earlycon: Enable earlycon without command line param")
setup_earlycon() will loop __earlycon_table with pointer to earlycon_id,
for (match = __earlycon_table; match->name[0]; match++) {
size_t len = strlen(match->name);

if (strncmp(buf, match->name, len))
continue;

but match size (size of struct earlycon_id) is only 0x18. so will point to
wrong place for next match and will get random result.

Make the earlycon_table section have pointer to earlycon_id struct instead.

Fixes: commit 470ca0de69fe ("serial: earlycon: Enable earlycon without command line param")
Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
drivers/tty/serial/earlycon.c | 13 +++++++------
include/asm-generic/vmlinux.lds.h | 8 ++++----
include/linux/serial_core.h | 8 +++++---
3 files changed, 16 insertions(+), 13 deletions(-)

Index: linux-2.6/include/linux/serial_core.h
===================================================================
--- linux-2.6.orig/include/linux/serial_core.h
+++ linux-2.6/include/linux/serial_core.h
@@ -349,10 +349,12 @@ extern int of_setup_earlycon(unsigned lo
int (*setup)(struct earlycon_device *, const char *));

#define EARLYCON_DECLARE(_name, func) \
- static const struct earlycon_id __earlycon_##_name \
- __used __section(__earlycon_table) \
+ static struct earlycon_id __earlycon_##_name __initdata \
= { .name = __stringify(_name), \
- .setup = func }
+ .setup = func }; \
+ static struct earlycon_id *__p_earlycon_##_name __used \
+ __aligned(sizeof(struct earlycon_id *)) \
+ __section(__earlycon_table) = { &__earlycon_##_name }

#define OF_EARLYCON_DECLARE(name, compat, fn) \
_OF_DECLARE(earlycon, name, compat, fn, void *)
Index: linux-2.6/drivers/tty/serial/earlycon.c
===================================================================
--- linux-2.6.orig/drivers/tty/serial/earlycon.c
+++ linux-2.6/drivers/tty/serial/earlycon.c
@@ -37,9 +37,8 @@ static struct earlycon_device early_cons
.con = &early_con,
};

-extern struct earlycon_id __earlycon_table[];
-static const struct earlycon_id __earlycon_table_sentinel
- __used __section(__earlycon_table_end);
+extern struct earlycon_id *__start_earlycon_table[];
+extern struct earlycon_id *__stop_earlycon_table[];

static const struct of_device_id __earlycon_of_table_sentinel
__used __section(__earlycon_of_table_end);
@@ -103,7 +102,7 @@ static int __init parse_options(struct e
return 0;
}

-static int __init register_earlycon(char *buf, const struct earlycon_id *match)
+static int __init register_earlycon(char *buf, struct earlycon_id *match)
{
int err;
struct uart_port *port = &early_console_dev.port;
@@ -147,7 +146,7 @@ static int __init register_earlycon(char
*/
int __init setup_earlycon(char *buf)
{
- const struct earlycon_id *match;
+ struct earlycon_id **pmatch;

if (!buf || !buf[0])
return -EINVAL;
@@ -155,7 +154,9 @@ int __init setup_earlycon(char *buf)
if (early_con.flags & CON_ENABLED)
return -EALREADY;

- for (match = __earlycon_table; match->name[0]; match++) {
+ for (pmatch = __start_earlycon_table; pmatch < __stop_earlycon_table;
+ pmatch++) {
+ struct earlycon_id *match = *pmatch;
size_t len = strlen(match->name);

if (strncmp(buf, match->name, len))
Index: linux-2.6/include/asm-generic/vmlinux.lds.h
===================================================================
--- linux-2.6.orig/include/asm-generic/vmlinux.lds.h
+++ linux-2.6/include/asm-generic/vmlinux.lds.h
@@ -151,10 +151,10 @@
#endif

#ifdef CONFIG_SERIAL_EARLYCON
-#define EARLYCON_TABLE() . = ALIGN(8); \
- VMLINUX_SYMBOL(__earlycon_table) = .; \
- *(__earlycon_table) \
- *(__earlycon_table_end)
+#define EARLYCON_TABLE() . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start_earlycon_table) = .; \
+ *(__earlycon_table) \
+ VMLINUX_SYMBOL(__stop_earlycon_table) = .;
#else
#define EARLYCON_TABLE()
#endif