linux-kernel - Re: [PATCH 1/2] panfrost: Make sure GPU is powered on when reading GPU_LATEST_FLUSH

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Date:   Fri, 19 Jun 2020 09:52:22 +0100
From:   Steven Price <steven.price@....com>
To:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Rob Herring <robh@...nel.org>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 1/2] panfrost: Make sure GPU is powered on when reading
 GPU_LATEST_FLUSH_ID

On 11/06/2020 09:58, Tomeu Vizoso wrote:
> Bifrost devices do support the flush reduction feature, so on first job
> submit we were trying to read the register while still powered off.
> 
> If the GPU is powered off, the feature doesn't bring any benefit, so
> don't try to read.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>

Reviewed-by: Steven Price <steven.price@....com>

> ---
>   drivers/gpu/drm/panfrost/panfrost_gpu.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index f2c1ddc41a9b..e0f190e43813 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -10,6 +10,7 @@
>   #include <linux/io.h>
>   #include <linux/iopoll.h>
>   #include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
>   
>   #include "panfrost_device.h"
>   #include "panfrost_features.h"
> @@ -368,7 +369,16 @@ void panfrost_gpu_fini(struct panfrost_device *pfdev)
>   
>   u32 panfrost_gpu_get_latest_flush_id(struct panfrost_device *pfdev)
>   {
> -	if (panfrost_has_hw_feature(pfdev, HW_FEATURE_FLUSH_REDUCTION))
> -		return gpu_read(pfdev, GPU_LATEST_FLUSH_ID);
> +	u32 flush_id;
> +
> +	if (panfrost_has_hw_feature(pfdev, HW_FEATURE_FLUSH_REDUCTION)) {
> +		/* Flush reduction only makes sense when the GPU is kept powered on between jobs */
> +		if (pm_runtime_get_if_in_use(pfdev->dev)) {
> +			flush_id = gpu_read(pfdev, GPU_LATEST_FLUSH_ID);
> +			pm_runtime_put(pfdev->dev);
> +			return flush_id;
> +		}
> +	}
> +
>   	return 0;
>   }
>