linux-kernel - Re: [PATCH] drm/panfrost: Remove core stack power management

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Message-ID: <20200109134351.GA3053@kevin>
Date:   Thu, 9 Jan 2020 08:43:51 -0500
From:   Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
To:     Steven Price <steven.price@....com>
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH] drm/panfrost: Remove core stack power management

A-b

On Thu, Jan 09, 2020 at 01:31:04PM +0000, Steven Price wrote:
> Explict management of the GPU's core stacks is only necessary in the
> case of a broken integration with the PDC. Since there are no known
> platforms which have such a broken integration let's remove the explict
> control from the driver since this apparently causes problems on other
> platforms and will have a small performance penality.
> 
> The out of tree mali_kbase driver contains this text regarding
> controlling the core stack (CONFIGMALI_CORESTACK):
> 
>   Enabling this feature on supported GPUs will let the driver powering
>   on/off the GPU core stack independently without involving the Power
>   Domain Controller. This should only be enabled on platforms which
>   integration of the PDC to the Mali GPU is known to be problematic.
>   This feature is currently only supported on t-Six and t-HEx GPUs.
> 
>   If unsure, say N.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_gpu.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index 8822ec13a0d6..460fc190de6e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -309,10 +309,6 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
>  	ret = readl_relaxed_poll_timeout(pfdev->iomem + L2_READY_LO,
>  		val, val == pfdev->features.l2_present, 100, 1000);
>  
> -	gpu_write(pfdev, STACK_PWRON_LO, pfdev->features.stack_present);
> -	ret |= readl_relaxed_poll_timeout(pfdev->iomem + STACK_READY_LO,
> -		val, val == pfdev->features.stack_present, 100, 1000);
> -
>  	gpu_write(pfdev, SHADER_PWRON_LO, pfdev->features.shader_present);
>  	ret |= readl_relaxed_poll_timeout(pfdev->iomem + SHADER_READY_LO,
>  		val, val == pfdev->features.shader_present, 100, 1000);
> @@ -329,7 +325,6 @@ void panfrost_gpu_power_off(struct panfrost_device *pfdev)
>  {
>  	gpu_write(pfdev, TILER_PWROFF_LO, 0);
>  	gpu_write(pfdev, SHADER_PWROFF_LO, 0);
> -	gpu_write(pfdev, STACK_PWROFF_LO, 0);
>  	gpu_write(pfdev, L2_PWROFF_LO, 0);
>  }
>  
> -- 
> 2.20.1
> 

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