Re: [PATCH 2/2] [media] exynos-gsc: Fix imprecise external abort due disabled power domain

[Javier Martinez Canillas]

Hello Marek,

Thanks a lot for your feedback.

On 01/19/2017 11:17 AM, Marek Szyprowski wrote:
> Hi Javier,
> 
> On 2017-01-18 01:30, Javier Martinez Canillas wrote:
>> Commit 15f90ab57acc ("[media] exynos-gsc: Make driver functional when
>> CONFIG_PM is unset") removed the implicit dependency that the driver
>> had with CONFIG_PM, since it relied on the config option to be enabled.
>>
>> In order to work with !CONFIG_PM, the GSC reset logic that happens in
>> the runtime resume callback had to be executed on the probe function.
>>
>> The problem is that if CONFIG_PM is enabled, the power domain for the
>> GSC could be disabled and so an attempt to write to the GSC_SW_RESET
>> register leads to an unhandled fault / imprecise external abort error:
> 
> Driver core ensures that driver's probe() is called with respective power
> domain turned on, so this is not the right reason for the proposed change.
>

Ok, I misunderstood the relationship between runtime PM and the power domains
then. I thought the power domains were only powered on when the runtime PM
framework resumed an associated device (i.e: pm_runtime_get_sync() is called).

But even if this isn't the case, shouldn't the reset in probe only be needed
if CONFIG_PM isn't enabled? (IOW, $SUBJECT but with another commit message).

>> [   10.178825] Unhandled fault: imprecise external abort (0x1406) at 0x00000000
>> [   10.186982] pgd = ed728000
>> [   10.190847] [00000000] *pgd=00000000
>> [   10.195553] Internal error: : 1406 [#1] PREEMPT SMP ARM
>> [   10.229761] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>> [   10.237134] task: ed49e400 task.stack: ed724000
>> [   10.242934] PC is at gsc_wait_reset+0x5c/0x6c [exynos_gsc]
>> [   10.249710] LR is at gsc_probe+0x300/0x33c [exynos_gsc]
>> [   10.256139] pc : [<bf2429e0>]    lr : [<bf240734>]    psr: 60070013
>> [   10.256139] sp : ed725d30  ip : 00000000  fp : 00000001
>> [   10.271492] r10: eea74800  r9 : ecd6a2c0  r8 : ed7d8854
>> [   10.277912] r7 : ed7d8c08  r6 : ed7d8810  r5 : ffff8ecd  r4 : c0c03900
>> [   10.285664] r3 : 00000000  r2 : 00000001  r1 : ed7d8b98  r0 : ed7d8810
>>
>> So only do a GSC reset if CONFIG_PM is disabled, since if is enabled the
>> runtime PM resume callback will be called by the VIDIOC_STREAMON ioctl,
>> making the reset in probe unneeded.
>>
>> Fixes: 15f90ab57acc ("[media] exynos-gsc: Make driver functional when CONFIG_PM is unset")
>> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
> 
> Frankly, I don't get why this change is needed.
>

Yes, it seems $SUBJECT is just papering over the real issue. There's
something really wrong with the Exynos power domains, I see that PDs
can't be disabled by the genpd framework, exynos_pd_power_off() fail:

# dmesg | grep power-domain
[    4.893318] Power domain power-domain@10044020 disable failed
[    4.893342] Power domain power-domain@10044120 disable failed
[    4.893711] Power domain power-domain@10044000 disable failed
[   12.690052] Power domain power-domain@10044000 disable failed
[   12.703963] Power domain power-domain@10044000 disable failed

So PD are kept on even when unused / attached devices are suspended.
Only the mfc_pd (power-domain@10044060) is correctly turned off.

# cat /sys/kernel/debug/pm_genpd/pm_genpd_summary
domain                          status          slaves
    /device                                             runtime status
----------------------------------------------------------------------
power-domain@100440C0           on              
    /devices/platform/soc/14450000.mixer                active
    /devices/platform/soc/14530000.hdmi                 active
power-domain@10044120           on              
power-domain@10044060           off-0           
    /devices/platform/soc/11000000.codec                suspended
power-domain@10044020           on              
power-domain@10044000           on              
    /devices/platform/soc/13e00000.video-scaler         suspended
    /devices/platform/soc/13e10000.video-scaler         suspended

Also when removing the exynos_gsc driver, I get the same error:

# rmmod s5p_mfc
[  106.405972] s5p-mfc 11000000.codec: Removing 11000000.codec
# rmmod exynos_gsc
[  227.008559] Unhandled fault: imprecise external abort (0x1c06) at 0x00048e14
[  227.015116] pgd = ed5dc000
[  227.017213] [00048e14] *pgd=b17c6835
[  227.020889] Internal error: : 1c06 [#1] PREEMPT SMP ARM
...
[  227.241585] [<bf2429bc>] (gsc_wait_reset [exynos_gsc]) from [<bf24009c>] (gsc_runtime_resume+0x9c/0xec [exynos_gsc])
[  227.252331] [<bf24009c>] (gsc_runtime_resume [exynos_gsc]) from [<c042e488>] (genpd_runtime_resume+0x120/0x1d4)
[  227.262294] [<c042e488>] (genpd_runtime_resume) from [<c04241c0>] (__rpm_callback+0xc8/0x218)

# cat /sys/kernel/debug/pm_genpd/pm_genpd_summary
domain                          status          slaves
    /device                                             runtime status
----------------------------------------------------------------------
power-domain@100440C0           on              
    /devices/platform/soc/14450000.mixer                active
    /devices/platform/soc/14530000.hdmi                 active
power-domain@10044120           on              
power-domain@10044060           off-0           
power-domain@10044020           on              
power-domain@10044000           on              
    /devices/platform/soc/13e00000.video-scaler         suspended
    /devices/platform/soc/13e10000.video-scaler         resuming

This seems to be caused by some needed clocks to access the power domains
to be gated, since I don't get these erros when passing clk_ignore_unused
as parameter in the kernel command line.

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America