Date:   Wed, 22 Nov 2023 09:48:45 +0000
From:   Steven Price <steven.price@....com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Boris Brezillon <boris.brezillon@...labora.com>
Cc:     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 09:06, AngeloGioacchino Del Regno wrote:
> Il 21/11/23 18:08, Krzysztof Kozlowski ha scritto:
>> On 21/11/2023 17:55, Boris Brezillon wrote:
>>> On Tue, 21 Nov 2023 17:11:42 +0100
>>> AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>>> wrote:
>>>
>>>> Il 21/11/23 16:34, Krzysztof Kozlowski ha scritto:
>>>>> On 08/11/2023 14:20, Steven Price wrote:
>>>>>> On 02/11/2023 14:15, AngeloGioacchino Del Regno wrote:
>>>>>>> The layout of the registers {TILER,SHADER,L2}_PWROFF_LO, used to
>>>>>>> request
>>>>>>> powering off cores, is the same as the {TILER,SHADER,L2}_PWRON_LO
>>>>>>> ones:
>>>>>>> this means that in order to request poweroff of cores, we are
>>>>>>> supposed
>>>>>>> to write a bitmask of cores that should be powered off!
>>>>>>> This means that the panfrost_gpu_power_off() function has always
>>>>>>> been
>>>>>>> doing nothing.
>>>>>>>
>>>>>>> Fix powering off the GPU by writing a bitmask of the cores to
>>>>>>> poweroff
>>>>>>> to the relevant PWROFF_LO registers and then check that the
>>>>>>> transition
>>>>>>> (from ON to OFF) has finished by polling the relevant PWRTRANS_LO
>>>>>>> registers.
>>>>>>>
>>>>>>> While at it, in order to avoid code duplication, move the core mask
>>>>>>> logic from panfrost_gpu_power_on() to a new panfrost_get_core_mask()
>>>>>>> function, used in both poweron and poweroff.
>>>>>>>
>>>>>>> Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
>>>>>>> Signed-off-by: AngeloGioacchino Del Regno
>>>>>>> <angelogioacchino.delregno@...labora.com>
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> This commit was added to next recently but it causes "external
>>>>> abort on
>>>>> non-linefetch" during boot of my Odroid HC1 board.
>>>>>
>>>>> At least bisect points to it.
>>>>>
>>>>> If fixed, please add:
>>>>>
>>>>> Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>>>>
>>>>> [    4.861683] 8<--- cut here ---
>>>>> [    4.863429] Unhandled fault: external abort on non-linefetch
>>>>> (0x1008) at 0xf0c8802c
>>>>> [    4.871018] [f0c8802c] *pgd=433ed811, *pte=11800653, *ppte=11800453
>>>>> ...
>>>>> [    5.164010]  panfrost_gpu_irq_handler from
>>>>> __handle_irq_event_percpu+0xcc/0x31c
>>>>> [    5.171276]  __handle_irq_event_percpu from
>>>>> handle_irq_event+0x38/0x80
>>>>> [    5.177765]  handle_irq_event from handle_fasteoi_irq+0x9c/0x250
>>>>> [    5.183743]  handle_fasteoi_irq from
>>>>> generic_handle_domain_irq+0x28/0x38
>>>>> [    5.190417]  generic_handle_domain_irq from
>>>>> gic_handle_irq+0x88/0xa8
>>>>> [    5.196741]  gic_handle_irq from generic_handle_arch_irq+0x34/0x44
>>>>> [    5.202893]  generic_handle_arch_irq from __irq_svc+0x8c/0xd0
>>>>>
>>>>> Full log:
>>>>> https://krzk.eu/#/builders/21/builds/4392/steps/11/logs/serial0
>>>>>    
>>>>
>>>> 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 🙂
> 
> 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:
> 
> 
> ---
>  drivers/gpu/drm/panfrost/panfrost_gpu.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index 09f5e1563ebd..1c7276aaa182 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -429,21 +429,29 @@ void panfrost_gpu_power_off(struct panfrost_device
> *pfdev)
>      int ret;
>      u32 val;
> 
> -    gpu_write(pfdev, SHADER_PWROFF_LO, pfdev->features.shader_present &
> core_mask);
> +    gpu_write(pfdev, SHADER_PWROFF_LO, pfdev->features.shader_present);

Hopefully this one line change, and...

> +    gpu_write(pfdev, SHADER_PWROFF_HI, U32_MAX);
>      ret = readl_relaxed_poll_timeout(pfdev->iomem + SHADER_PWRTRANS_LO,
>                       val, !val, 1, 1000);
>      if (ret)
>          dev_err(pfdev->dev, "shader power transition timeout");
> 
>      gpu_write(pfdev, TILER_PWROFF_LO, pfdev->features.tiler_present);
> +    gpu_write(pfdev, TILER_PWROFF_HI, U32_MAX);
>      ret = readl_relaxed_poll_timeout(pfdev->iomem + TILER_PWRTRANS_LO,
>                       val, !val, 1, 1000);
>      if (ret)
>          dev_err(pfdev->dev, "tiler power transition timeout");
> 
> -    gpu_write(pfdev, L2_PWROFF_LO, pfdev->features.l2_present &
> core_mask);
> +    gpu_write(pfdev, L2_PWROFF_LO, pfdev->features.l2_present);

... this one are all that are actually needed - the rest should be
ignored as they affect cores that aren't present.

The Exynos 5422 SoC has a T628 MP6 - so two core groups which isn't a
particularly well supported configuration. But I'm not sure how we're
ending up with the second core group being powered up in the first
place. Even if it was left powered by something previous (e.g. the
bootloader) then the soft-reset during probe should cause them to power
down.

But it seems like a good idea to power off everything when powering
down, even if we didn't expect the cores to be on.

Boris also has a point that before cutting the power/clocks we should
really be synchronising with the IRQs - but that affects the follow on
patches not this one.

Steve

>      ret = readl_poll_timeout(pfdev->iomem + L2_PWRTRANS_LO,
> -                 val, !val, 0, 1000);
> +                     val, !val, 0, 1000);
> +    if (ret)
> +        dev_err(pfdev->dev, "l2_low power transition timeout");
> +
> +    gpu_write(pfdev, L2_PWROFF_HI, U32_MAX);
> +    ret = readl_poll_timeout(pfdev->iomem + L2_PWRTRANS_HI,
> +                     val, !val, 0, 1000);
>      if (ret)
>          dev_err(pfdev->dev, "l2 power transition timeout");
>  }

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