linux-kernel - Re: [PATCH v2] drm/panfrost: Ignore core_mask for poweroff and sync interrupts

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Date:   Thu, 23 Nov 2023 12:58:17 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        steven.price@....com
Cc:     boris.brezillon@...labora.com, robh@...nel.org,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/panfrost: Ignore core_mask for poweroff and sync
 interrupts

Il 23/11/23 12:57, Krzysztof Kozlowski ha scritto:
> On 23/11/2023 12:50, AngeloGioacchino Del Regno wrote:
>> Some SoCs may be equipped with a GPU containing two core groups
>> and this is exactly the case of Samsung's Exynos 5422 featuring
>> an ARM Mali-T628 MP6 GPU: the support for this GPU in Panfrost
>> is partial, as this driver currently supports using only one
>> core group and that's reflected on all parts of it, including
>> the power on (and power off, previously to this patch) function.
>>
>> The issue with this is that even though executing the soft reset
>> operation should power off all cores unconditionally, on at least
>> one platform we're seeing a crash that seems to be happening due
>> to an interrupt firing which may be because we are calling power
>> transition only on the first core group, leaving the second one
>> unchanged, or because ISR execution was pending before entering
>> the panfrost_gpu_power_off() function and executed after powering
>> off the GPU cores, or all of the above.
>>
>> Finally, solve this by introducing a new panfrost_gpu_suspend_irq()
>> helper function and changing the panfrost_device_suspend() flow to
>>   1. Mask and clear all interrupts: we don't need nor want any, as
>>      for power_off() we are polling PWRTRANS, but we anyway don't
>>      want GPU IRQs to fire while it is suspended/powered off;
>>   2. Call synchronize_irq() after that to make sure that any pending
>>      ISR is executed before powering off the GPU Shaders/Tilers/L2
>>      hence avoiding unpowered registers R/W; and
>>   3. Ignore the core_mask and ask the GPU to poweroff both core groups
>>
>> Of course it was also necessary to add a `irq` variable to `struct
>> panfrost_device` as we need to get that in panfrost_gpu_power_off()
>> for calling synchronize_irq() on it.
>>
>> Fixes: 22aa1a209018 ("drm/panfrost: Really power off GPU cores in panfrost_gpu_power_off()")
>> [Regression detected on Odroid HC1, Exynos5422, Mali-T628 MP6]
>> Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>
>> Changes in v2:
>>   - Fixed the commit hash of "Really power off [...]"
>>   - Actually based on a clean next-20231121
>>   - Renamed "irq" to "gpu_irq" as per Boris' suggestion
>>   - Moved the IRQ mask/clear/sync to a helper function and added
>>     a call to that in panfrost_device.c instead of doing that in
>>     panfrost_gpu_power_off().
>>
>> NOTE: I didn't split 1+2 from 3 as suggested by Boris, and I'm sending
>> this one without waiting for feedback on my reasons for that which I
>> explained as a reply to v1 because the former couldn't be applied to
>> linux-next, and I want to unblock Krzysztof ASAP to get this tested.
>>
> 
> This does not compile.
> 

I really have to take a break. My brain starts failing, as I can see.

Sorry.