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

[Yinghai Lu]

On Wed, Apr 1, 2015 at 8:22 PM, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> 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
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@xxxxxxxxxx>

---
 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