[PATCH v2] drm/exynos/mixer: fix MIXER shadow registry synchronisation code

[Marek Szyprowski]

Hi Inki,

On 2019-03-21 09:20, Inki Dae wrote:
> 19. 3. 19. 오후 10:05에 Andrzej Hajda 이(가) 쓴 글:
>> MIXER on Exynos5 SoCs uses different synchronisation method than Exynos4
>> to update internal state (shadow registers).
>> Apparently the driver implements it incorrectly. The rule should be
>> as follows:
>> - do not request updating registers until previous request was finished,
>>    ie. MXR_CFG_LAYER_UPDATE_COUNT must be 0.
>> - before setting registers synchronisation on VSYNC should be turned off,
>>    ie. MXR_STATUS_SYNC_ENABLE should be reset,
>> - after finishing MXR_STATUS_SYNC_ENABLE should be set again.
>> The patch hopefully implements it correctly.
>> Below sample kernel log from page fault caused by the bug:
>>
>> [   25.670038] exynos-sysmmu 14650000.sysmmu: 14450000.mixer: PAGE FAULT occurred at 0x2247b800
>> [   25.677888] ------------[ cut here ]------------
>> [   25.682164] kernel BUG at ../drivers/iommu/exynos-iommu.c:450!
>> [   25.687971] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
>> [   25.693778] Modules linked in:
>> [   25.696816] CPU: 5 PID: 1553 Comm: fb-release_test Not tainted 5.0.0-rc7-01157-g5f86b1566bdd #136
>> [   25.705646] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>> [   25.711710] PC is at exynos_sysmmu_irq+0x1c0/0x264
>> [   25.716470] LR is at lock_is_held_type+0x44/0x64
>>
>> v2: added missing MXR_CFG_LAYER_UPDATE bit setting in mixer_enable_sync
>>
>> Reported-by: Marian Mihailescu <mihailescu2m at gmail.com>
>> Signed-off-by: Andrzej Hajda <a.hajda at samsung.com>
>> ---
>> Hi Inki and Marian,
>>
>> This is fixed version of my previous patch. The only difference is
>> added missing MXR_CFG_LAYER_UPDATE setting in mixer_enable_sync.
>> I hope this time it is correct. It should solve one page fault issue
>> in MIXER, Marek is preparing fix for another issue (to low clock set by
>> devfreq). I hope with both patches page faults will not happen anymore ;)
> With this patch modetest worked well.
> BTW, this change may affect Exynos4 series - which have different synchronization way to update shadow registers - so could you or someone else who has Exynos4xxx based board check it on Odroid-u3 board? I have no board. :(

Andrzej's patch has been tested on Exynos4412 too. HDMI display works 
fine on Odroid U3.

...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland