linux-kernel - Re: [PATCH] drm/panfrost: Really power off GPU cores in panfrost_gpu_power

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Message-ID: <39e9514b-087c-42eb-8d0e-f75dc620e954@linaro.org>
Date:   Wed, 22 Nov 2023 10:29:45 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Boris Brezillon <boris.brezillon@...labora.com>
Cc:     Steven Price <steven.price@....com>, tzimmermann@...e.de,
        linux-kernel@...r.kernel.org, mripard@...nel.org,
        dri-devel@...ts.freedesktop.org, wenst@...omium.org,
        kernel@...labora.com,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] drm/panfrost: Really power off GPU cores in
 panfrost_gpu_power_off()

On 22/11/2023 10:06, AngeloGioacchino Del Regno wrote:

>>>>>    
>>>>
>>>> Hey Krzysztof,
>>>>
>>>> This is interesting. It might be about the cores that are missing from the partial
>>>> core_mask raising interrupts, but an external abort on non-linefetch is strange to
>>>> see here.
>>>
>>> I've seen such external aborts in the past, and the fault type has
>>> often been misleading. It's unlikely to have anything to do with a
>>
>> Yeah, often accessing device with power or clocks gated.
>>
> 
> Except my commit does *not* gate SoC power, nor SoC clocks 🙂

It could be that something (like clocks or power supplies) was missing
on this board/SoC, which was not critical till your patch came.

> 
> What the "Really power off ..." commit does is to ask the GPU to internally power
> off the shaders, tilers and L2, that's why I say that it is strange to see that
> kind of abort.
> 
> The GPU_INT_CLEAR GPU_INT_STAT, GPU_FAULT_STATUS and GPU_FAULT_ADDRESS_{HI/LO}
> registers should still be accessible even with shaders, tilers and cache OFF.
> 
> Anyway, yes, synchronizing IRQs before calling the poweroff sequence would also
> work, but that'd add up quite a bit of latency on the runtime_suspend() call, so
> in this case I'd be more for avoiding to execute any register r/w in the handler
> by either checking if the GPU is supposed to be OFF, or clearing interrupts, which
> may not work if those are generated after the execution of the poweroff function.
> Or we could simply disable the irq after power_off, but that'd be hacky (as well).
> 
> 
> Let's see if asking to poweroff *everything* works:

Worked.

Best regards,
Krzysztof