linux-kernel - Re: [PATCH] drm/panfrost: Add support for non-existent reset node

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Date:   Mon, 2 Nov 2020 09:11:43 +0000
From:   Steven Price <steven.price@....com>
To:     Yejune Deng <yejune.deng@...il.com>, robh@...nel.org,
        tomeu.vizoso@...labora.com, alyssa.rosenzweig@...labora.com,
        airlied@...ux.ie, daniel@...ll.ch, p.zabel@...gutronix.de
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panfrost: Add support for non-existent reset node

On 02/11/2020 08:54, Yejune Deng wrote:
> Some dts hasn't no reset node, is should ok.
> 
> Signed-off-by: Yejune Deng <yejune.deng@...il.com>
> ---
>   drivers/gpu/drm/panfrost/panfrost_device.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index ea8d318..a982878 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -18,7 +18,12 @@
>   
>   static int panfrost_reset_init(struct panfrost_device *pfdev)
>   {
> -	pfdev->rstc = devm_reset_control_array_get(pfdev->dev, false, true);
> +	pfdev->rstc = devm_reset_control_array_get_optional_exclusive(pfdev->dev);

This change is fine - it should have no functional change and makes the 
code more readable.

> +	if (!pfdev->rstc) {
> +		dev_info(pfdev->dev, "reset does not exist\n");

I don't think this output is particularly useful.

> +		return 0;

The early return isn't necessary. IS_ERR(NULL) is false, and 
reset_control_deassert() deals fine with NULL, so the path below would 
be fine.

> +	}
> +
>   	if (IS_ERR(pfdev->rstc)) {
>   		dev_err(pfdev->dev, "get reset failed %ld\n", PTR_ERR(pfdev->rstc));
>   		return PTR_ERR(pfdev->rstc);
> @@ -29,7 +34,8 @@ static int panfrost_reset_init(struct panfrost_device *pfdev)
>   
>   static void panfrost_reset_fini(struct panfrost_device *pfdev)
>   {
> -	reset_control_assert(pfdev->rstc);
> +	if (pfdev->rstc)
> +		reset_control_assert(pfdev->rstc);

reset_control_assert() deals fine with a NULL input, so this is unneeded.

>   }
>   
>   static int panfrost_clk_init(struct panfrost_device *pfdev)
> 

Have you actually seen a problem on a platform without a reset node - it 
works fine for me and I can't see any functional change with this patch.

Steve