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Date:   Thu, 23 Nov 2023 16:40:19 +0100
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Cc:     steven.price@arm.com, robh@kernel.org,
        maarten.lankhorst@linux.intel.com, mripard@kernel.org,
        tzimmermann@suse.de, airlied@gmail.com, daniel@ffwll.ch,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        krzysztof.kozlowski@linaro.org, kernel@collabora.com
Subject: Re: [PATCH] drm/panfrost: Ignore core_mask for poweroff and sync
 interrupts
Message-ID: <20231123164019.629c91f9@collabora.com>
In-Reply-To: <43cc8641-6a60-41d9-b8f2-32227235702a@collabora.com>
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On Thu, 23 Nov 2023 16:14:12 +0100
AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
wrote:

> Il 23/11/23 14:51, Boris Brezillon ha scritto:
> > On Thu, 23 Nov 2023 14:24:57 +0100
> > AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> > wrote:
> >   
> >>>>
> >>>> So, while I agree that it'd be slightly more readable as a diff if those
> >>>> were two different commits I do have reasons against splitting.....  
> >>>
> >>> If we just need a quick fix to avoid PWRTRANS interrupts from kicking
> >>> in when we power-off the cores, I think we'd be better off dropping
> >>> GPU_IRQ_POWER_CHANGED[_ALL] from the value we write to GPU_INT_MASK
> >>> at [re]initialization time, and then have a separate series that fixes
> >>> the problem more generically.
> >>>      
> >>
> >> But that didn't work:
> >> https://lore.kernel.org/all/d95259b8-10cf-4ded-866c-47cbd2a44f84@linaro.org/  
> > 
> > I meant, your 'ignore-core_mask' fix + the
> > 'drop GPU_IRQ_POWER_CHANGED[_ALL] in GPU_INT_MASK' one.
> > 
> > So,
> > 
> > https://lore.kernel.org/all/4c73f67e-174c-497e-85a5-cb053ce657cb@collabora.com/
> > +
> > https://lore.kernel.org/all/d95259b8-10cf-4ded-866c-47cbd2a44f84@linaro.org/
> >   
> >>
> >>
> >> ...while this "full" solution worked:
> >> https://lore.kernel.org/all/39e9514b-087c-42eb-8d0e-f75dc620e954@linaro.org/
> >>
> >> https://lore.kernel.org/all/5b24cc73-23aa-4837-abb9-b6d138b46426@linaro.org/
> >>
> >>
> >> ...so this *is* a "quick fix" already... :-)  
> > 
> > It's a half-baked solution for the missing irq-synchronization-on-suspend
> > issue IMHO. I understand why you want it all in one patch that can serve
> > as a fix for 123b431f8a5c ("drm/panfrost: Really power off GPU cores in
> > panfrost_gpu_power_off()"), which is why I'm suggesting to go for an
> > even simpler diff (see below), and then fully address the
> > irq-synhronization-on-suspend issue in a follow-up patchset.
> >   
> > --->8---  
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> > index 09f5e1563ebd..6e2d7650cc2b 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> > @@ -78,7 +78,10 @@ int panfrost_gpu_soft_reset(struct panfrost_device *pfdev)
> >          }
> >   
> >          gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_MASK_ALL);
> > -       gpu_write(pfdev, GPU_INT_MASK, GPU_IRQ_MASK_ALL);

We probably want a comment here:

	/* Only enable the interrupts we care about. */

> > +       gpu_write(pfdev, GPU_INT_MASK,
> > +                 GPU_IRQ_MASK_ERROR |
> > +                 GPU_IRQ_PERFCNT_SAMPLE_COMPLETED |
> > +                 GPU_IRQ_CLEAN_CACHES_COMPLETED);
> >     
> 
> ...but if we do that, the next patch(es) will contain a partial revert of this
> commit, putting back this to gpu_write(pfdev, GPU_INT_MASK, GPU_IRQ_MASK_ALL)...

Why should we revert it? We're not processing the PWRTRANS interrupts
in the interrupt handler, those should never have been enabled in the
first place. The only reason we'd want to revert that change is if we
decide to do have interrupt-based waits in the poweron/off
implementation, which, as far as I'm aware, is not something we intend
to do any time soon.

> 
> I'm not sure that it's worth changing this like that, then changing it back right
> after :-\
> 
> Anyway, if anyone else agrees with doing it and then partially revert, I have no
> issues going with this one instead; what I care about ultimately is resolving the
> regression ASAP :-)
> 
> Cheers,
> Angelo
> 
> >          /*
> >           * All in-flight jobs should have released their cycle
> > @@ -425,11 +428,10 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
> >   
> >   void panfrost_gpu_power_off(struct panfrost_device *pfdev)
> >   {
> > -       u64 core_mask = panfrost_get_core_mask(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);
> >          ret = readl_relaxed_poll_timeout(pfdev->iomem + SHADER_PWRTRANS_LO,
> >                                           val, !val, 1, 1000);
> >          if (ret)
> > @@ -441,7 +443,7 @@ void panfrost_gpu_power_off(struct panfrost_device *pfdev)
> >          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);
> >          ret = readl_poll_timeout(pfdev->iomem + L2_PWRTRANS_LO,
> >                                   val, !val, 0, 1000);
> >          if (ret)
> > 
> >   
>