Subject: [PATCH] ARM: omap2: am437x: rollback to use omap3_gptimer_timer_init()

From: [email-masked] (Grygorii Strashko)
Date: Tue, 12 Apr 2016 21:30:32 +0300

On 04/12/2016 07:04 PM, Tony Lindgren wrote:
> * Grygorii Strashko <[email-masked]> [160412 03:44]:
>> 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().
> 
> 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-masked]>
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
    
    Use gptimer as clocksource instead, as is done in the case of AM335x
    (which does not have a SyncTimer). With this, system time keeping works
    accurately.
    
    Signed-off-by: Rajendra Nayak <[email-masked]>
    Signed-off-by: Lokesh Vutla <[email-masked]>
    Signed-off-by: Tony Lindgren <[email-masked]>

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

-- 
regards,
-grygorii