linux-kernel - Re: [PATCH v2 2/6] drm/panfrost: Tighten polling for soft reset and power on

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Date:   Wed, 8 Nov 2023 15:44:44 +0000
From:   Steven Price <steven.price@....com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        boris.brezillon@...labora.com
Cc:     robh@...nel.org, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, wenst@...omium.org,
        kernel@...labora.com
Subject: Re: [PATCH v2 2/6] drm/panfrost: Tighten polling for soft reset and
 power on

On 02/11/2023 14:26, AngeloGioacchino Del Regno wrote:
> In many cases, soft reset takes more than 1 microsecond, but definitely
> less than 10; moreover in the poweron flow, tilers, shaders and l2 will
> become ready (each) in less than 10 microseconds as well.
> 
> Even in the cases (at least on my platforms, rarely) in which those take
> more than 10 microseconds, it's very unlikely to see both soft reset and
> poweron to take more than 70 microseconds.
> 
> Shorten the polling delay to 10 microseconds to consistently reduce the
> runtime resume time of the GPU.
> 
> As an indicative example, measurements taken on a MediaTek MT8195 SoC
> 
> Average runtime resume time in nanoseconds before this commit:
> GDM, user selection up/down:            88435ns
> GDM, Text Entry (typing user/password): 91489ns
> GNOME Desktop, idling, GKRELLM running: 73200ns
> 
> After this commit:
> 
> GDM: user selection up/down:            26690ns
> GDM: Text Entry (typing user/password): 27917ns
> GNOME Desktop, idling, GKRELLM running:	25304ns
> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

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

> ---
>  drivers/gpu/drm/panfrost/panfrost_gpu.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index 7e9e2cf26e4d..e264e8c2252d 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -63,7 +63,7 @@ int panfrost_gpu_soft_reset(struct panfrost_device *pfdev)
>  
>  	gpu_write(pfdev, GPU_CMD, GPU_CMD_SOFT_RESET);
>  	ret = readl_relaxed_poll_timeout(pfdev->iomem + GPU_INT_RAWSTAT,
> -		val, val & GPU_IRQ_RESET_COMPLETED, 100, 10000);
> +		val, val & GPU_IRQ_RESET_COMPLETED, 10, 10000);
>  	if (ret) {
>  		dev_err(pfdev->dev, "gpu soft reset timed out, attempting hard reset\n");
>  
> @@ -403,7 +403,7 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
>  	gpu_write(pfdev, L2_PWRON_LO, pfdev->features.l2_present & core_mask);
>  	ret = readl_relaxed_poll_timeout(pfdev->iomem + L2_READY_LO,
>  		val, val == (pfdev->features.l2_present & core_mask),
> -		100, 20000);
> +		10, 20000);
>  	if (ret)
>  		dev_err(pfdev->dev, "error powering up gpu L2");
>  
> @@ -411,13 +411,13 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
>  		  pfdev->features.shader_present & core_mask);
>  	ret = readl_relaxed_poll_timeout(pfdev->iomem + SHADER_READY_LO,
>  		val, val == (pfdev->features.shader_present & core_mask),
> -		100, 20000);
> +		10, 20000);
>  	if (ret)
>  		dev_err(pfdev->dev, "error powering up gpu shader");
>  
>  	gpu_write(pfdev, TILER_PWRON_LO, pfdev->features.tiler_present);
>  	ret = readl_relaxed_poll_timeout(pfdev->iomem + TILER_READY_LO,
> -		val, val == pfdev->features.tiler_present, 100, 1000);
> +		val, val == pfdev->features.tiler_present, 10, 1000);
>  	if (ret)
>  		dev_err(pfdev->dev, "error powering up gpu tiler");
>  }