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authorPaul Walmsley <paul@pwsan.com>2010-11-24 16:49:05 -0700
committerTony Lindgren <tony@atomide.com>2010-11-24 16:14:30 -0800
commit0d8e2d0dad98a693bad88aea6876ac8b94ad95c6 (patch)
treed2b5bc9475d040b677de7b974300c0ad1222ae7c /arch/arm/mach-omap2/pm24xx.c
parentf910043ce00791c06afc3789278447c4e88670ea (diff)
downloadlinux-2.6.38-lt-ux500-0d8e2d0dad98a693bad88aea6876ac8b94ad95c6.tar.gz
OMAP2+: PM/serial: hold console semaphore while OMAP UARTs are disabled
The console semaphore must be held while the OMAP UART devices are disabled, lest a console write cause an ARM abort (and a kernel crash) when the underlying console device is inaccessible. These crashes only occur when the console is on one of the OMAP internal serial ports. While this problem has been latent in the PM idle loop for some time, the crash was not triggerable with an unmodified kernel until commit 6f251e9db1093c187addc309b5f2f7fe3efd2995 ("OMAP: UART: omap_device conversions, remove implicit 8520 assumptions"). After this patch, a console write often occurs after the console UART has been disabled in the idle loop, crashing the system. Several users have encountered this bug: http://www.mail-archive.com/linux-omap@vger.kernel.org/msg38396.html http://www.mail-archive.com/linux-omap@vger.kernel.org/msg36602.html The same commit also introduced new code that disabled the UARTs during init, in omap_serial_init_port(). The kernel will also crash in this code when earlyconsole and extra debugging is enabled: http://www.mail-archive.com/linux-omap@vger.kernel.org/msg36411.html The minimal fix for the -rc series is to hold the console semaphore while the OMAP UARTs are disabled. This is a somewhat overbroad fix, since the console may not be located on an OMAP UART, as is the case with the GPMC UART on Zoom3. While it is technically possible to determine which devices the console or earlyconsole is actually running on, it is not a trivial problem to solve, and the code to do so is not really appropriate for the -rc series. The right long-term fix is to ensure that no code outside of the OMAP serial driver can disable an OMAP UART. As I understand it, code to implement this is under development by TI. This patch is a collaboration between Paul Walmsley <paul@pwsan.com> and Tony Lindgren <tony@atomide.com>. Thanks to Ming Lei <tom.leiming@gmail.com> and Pramod <pramod.gurav@ti.com> for their feedback on earlier versions of this patch. Signed-off-by: Paul Walmsley <paul@pwsan.com> Signed-off-by: Tony Lindgren <tony@atomide.com> Acked-by: Kevin Hilman <khilman@deeprootsystems.com> Cc: Ming Lei <tom.leiming@gmail.com> Cc: Pramod <pramod.gurav@ti.com> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Cc: Jean Pihet <jean.pihet@newoldbits.com> Cc: Govindraj.R <govindraj.raja@ti.com>
Diffstat (limited to 'arch/arm/mach-omap2/pm24xx.c')
-rw-r--r--arch/arm/mach-omap2/pm24xx.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/arm/mach-omap2/pm24xx.c b/arch/arm/mach-omap2/pm24xx.c
index a40457d8192..c85923e56b8 100644
--- a/arch/arm/mach-omap2/pm24xx.c
+++ b/arch/arm/mach-omap2/pm24xx.c
@@ -30,6 +30,7 @@
#include <linux/irq.h>
#include <linux/time.h>
#include <linux/gpio.h>
+#include <linux/console.h>
#include <asm/mach/time.h>
#include <asm/mach/irq.h>
@@ -118,6 +119,10 @@ static void omap2_enter_full_retention(void)
if (omap_irq_pending())
goto no_sleep;
+ /* Block console output in case it is on one of the OMAP UARTs */
+ if (try_acquire_console_sem())
+ goto no_sleep;
+
omap_uart_prepare_idle(0);
omap_uart_prepare_idle(1);
omap_uart_prepare_idle(2);
@@ -131,6 +136,8 @@ static void omap2_enter_full_retention(void)
omap_uart_resume_idle(1);
omap_uart_resume_idle(0);
+ release_console_sem();
+
no_sleep:
if (omap2_pm_debug) {
unsigned long long tmp;