ARM: omap2: am437x: rollback to use omap3_gptimer_timer_init()

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

[1] http://www.spinics.net/lists/linux-omap/msg127425.html

Cc Felipe Balbi <[email protected]>

Cc Lokesh Vutla <[email protected]>

Reported-by Cooper Jr., Franklin <[email protected]>

Signed-off-by Grygorii Strashko <[email protected]>

---
 arch/arm/mach-omap2/board-generic.c | 2 +-
 arch/arm/mach-omap2/timer.c         | 7 +++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

arch/arm/mach-omap2/board-generic.c +1 -1

index bab814d..60f5e83 100644
@@ -306,7 +306,7 @@ DT_MACHINE_START(AM43_DT, "Generic AM43 (Flattened Device Tree)")
 	.init_late	= am43xx_init_late,
 	.init_irq	= omap_gic_of_init,
 	.init_machine	= omap_generic_init,
-	.init_time	= omap4_local_timer_init,
+	.init_time	= omap3_gptimer_timer_init,
 	.dt_compat	= am43_boards_compat,
 	.restart	= omap44xx_restart,
 MACHINE_END

arch/arm/mach-omap2/timer.c +5 -2

index 6261e93..7cc055c 100644
@@ -500,16 +500,19 @@ void __init omap3_secure_sync32k_timer_init(void)
 }
 #endif /* CONFIG_ARCH_OMAP3 */
 
-#if defined(CONFIG_ARCH_OMAP3) || defined(CONFIG_SOC_AM33XX)
+#if defined(CONFIG_ARCH_OMAP3) || defined(CONFIG_SOC_AM33XX) || \
+	defined(CONFIG_SOC_AM43XX)
 void __init omap3_gptimer_timer_init(void)
 {
 	__omap_sync32k_timer_init(2, "timer_sys_ck", NULL,
 			1, "timer_sys_ck", "ti,timer-alwon", true);
+	if (of_have_populated_dt())
+		clocksource_probe();
 }
 #endif
 
 #if defined(CONFIG_ARCH_OMAP4) || defined(CONFIG_SOC_OMAP5) ||		\
-	defined(CONFIG_SOC_DRA7XX) || defined(CONFIG_SOC_AM43XX)
+	defined(CONFIG_SOC_DRA7XX)
 static void __init omap4_sync32k_timer_init(void)
 {
 	__omap_sync32k_timer_init(1, "timer_32k_ck", "ti,timer-alwon",

Quoted 10 lines · Grygorii Strashko

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Quoted 2 lines

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

I tested this patch and was not able to reproduce this issue after rebooting the AM437 GP evm 30 times. I then tried without this patch and the issue showed up after rebooting the board for the 5th time.

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

Quoted 10 lines · Grygorii Strashko

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Quoted 2 lines

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

I thought only the ePOS EVM does not have the 32k clock available? Maybe this is the the old sync timer autocorrection drift issue?

Quoted 11 lines · Tony Lindgren

Quoted 10 lines · Grygorii Strashko

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Quoted 6 lines

Quoted 2 lines

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

I thought only the ePOS EVM does not have the 32k clock available? Maybe this is the the old sync timer autocorrection drift issue?

May be, as i mentioned in [1] it could be errata same as for Watchdog Advisory 22 (or OMAP_TIMER_ERRATA_I103_I767).

But as per commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") there is no reason to use SyncTimer32K as clocksource any way (not only on epos):

commit 5b5c01359152f3ddaa1aa0e5d1141bc2b29ba2c5

Author: Rajendra Nayak <[email protected]>
Date:   Fri Feb 7 15:51:26 2014 +0530

ARM: OMAP2+: AM43x: Use gptimer as clocksource

The SyncTimer in AM43x is clocked using the following two sources:
1) An inaccuarte 32k clock (CLK_32KHZ) derived from PER DPLL, causing system time to go slowly (~10% deviation).
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2) external 32KHz RTC clock, which may not always be available on board like in the case of ePOS EVM

Quoted 30 lines · Grygorii Strashko

Quoted 11 lines · Tony Lindgren

Quoted 10 lines · Grygorii Strashko

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Quoted 6 lines

Quoted 2 lines

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

I thought only the ePOS EVM does not have the 32k clock available? Maybe this is the the old sync timer autocorrection drift issue?

May be, as i mentioned in [1] it could be errata same as for Watchdog Advisory 22 (or OMAP_TIMER_ERRATA_I103_I767).

But as per commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") there is no reason to use SyncTimer32K as clocksource any way (not only on epos):

commit 5b5c01359152f3ddaa1aa0e5d1141bc2b29ba2c5

Author: Rajendra Nayak <[email protected]>
Date:   Fri Feb 7 15:51:26 2014 +0530

Quoted 6 lines

ARM: OMAP2+: AM43x: Use gptimer as clocksource

The SyncTimer in AM43x is clocked using the following two sources:
1) An inaccuarte 32k clock (CLK_32KHZ) derived from PER DPLL, causing system time to go slowly (~10% deviation).
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Quoted 2 lines

2) external 32KHz RTC clock, which may not always be available on board like in the case of ePOS EVM

Quoted 31 lines · Tony Lindgren

Quoted 30 lines · Grygorii Strashko

Quoted 11 lines · Tony Lindgren

Quoted 10 lines · Grygorii Strashko

The commit 55ee7017ee31 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x") unintentionally changes the clocksource devices for AM437x from OMAP GP Timer to SyncTimer32K.

Unfortunately, the SyncTimer32K is starving from frequency deviation as mentioned in commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") and, as reported by Franklin [1], even its monotonic nature is under question (most probably there is a HW issue, but it's still under investigation).

Quoted 6 lines

Quoted 2 lines

Taking into account above facts It's reasonable to rollback to the use of omap3_gptimer_timer_init().

I thought only the ePOS EVM does not have the 32k clock available? Maybe this is the the old sync timer autocorrection drift issue?

May be, as i mentioned in [1] it could be errata same as for Watchdog Advisory 22 (or OMAP_TIMER_ERRATA_I103_I767).

But as per commit 5b5c01359152 ("ARM: OMAP2+: AM43x: Use gptimer as clocksource") there is no reason to use SyncTimer32K as clocksource any way (not only on epos):

commit 5b5c01359152f3ddaa1aa0e5d1141bc2b29ba2c5

Author: Rajendra Nayak <[email protected]>
Date:   Fri Feb 7 15:51:26 2014 +0530

Quoted 6 lines

Quoted 6 lines

ARM: OMAP2+: AM43x: Use gptimer as clocksource

The SyncTimer in AM43x is clocked using the following two sources:
1) An inaccuarte 32k clock (CLK_32KHZ) derived from PER DPLL, causing system time to go slowly (~10% deviation).
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I don't think this statement is right. If clock from PER DPLL is inaccurate then all the IPs which uses PER DPLL are in danger. It is the On-Chip 32K RC Osc clock that is not an accurate clock-source as per the design/spec.

Quoted 2 lines

Quoted 2 lines

2) external 32KHz RTC clock, which may not always be available on board like in the case of ePOS EVM

Also this 32KHz RTC clock is not enabled by default and is handled by RTC.

IMO, it is better to change the clock source of sync timer to CLK_32KHz(like it is done in case of am43x-epos). Or do you have any other reason to shift to gptimer?

From registers I can see that 32K synctimer is in no-idle mode