linux-kernel - Re: [PATCH v1 01/10] drm/panthor: Factor out GPU

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Message-ID: <6c01f00b-7be3-451e-8429-2c5036dfe103@arm.com>
Date: Mon, 20 Oct 2025 09:57:19 +0100
From: Steven Price <steven.price@....com>
To: Karunika Choo <karunika.choo@....com>, dri-devel@...ts.freedesktop.org
Cc: nd@....com, Boris Brezillon <boris.brezillon@...labora.com>,
 Liviu Dudau <liviu.dudau@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 01/10] drm/panthor: Factor out GPU_ID register read
 into separate function

On 14/10/2025 10:43, Karunika Choo wrote:
> Split the GPU_ID register read into its own helper function. The GPU_ID
> value will be used to enable architecture-specific behaviours, which may
> also affect how other registers (such as those used for gpu_info) are
> read.
> 
> This change separates the read operation so that subsequent code can
> depend on the intermediate result of processing the GPU_ID.
> 
> Signed-off-by: Karunika Choo <karunika.choo@....com>

I'd be very tempted to squash this into the next commit and simple read
the GPU ID at the beginning of panthor_hw_bind_device(). Is there any
reason not to?

Steve

> ---
>  drivers/gpu/drm/panthor/panthor_hw.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
> index 4f2858114e5e..326a9db0b5c2 100644
> --- a/drivers/gpu/drm/panthor/panthor_hw.c
> +++ b/drivers/gpu/drm/panthor/panthor_hw.c
> @@ -62,7 +62,6 @@ static void panthor_gpu_info_init(struct panthor_device *ptdev)
>  {
>  	unsigned int i;
>  
> -	ptdev->gpu_info.gpu_id = gpu_read(ptdev, GPU_ID);
>  	ptdev->gpu_info.csf_id = gpu_read(ptdev, GPU_CSF_ID);
>  	ptdev->gpu_info.gpu_rev = gpu_read(ptdev, GPU_REVID);
>  	ptdev->gpu_info.core_features = gpu_read(ptdev, GPU_CORE_FEATURES);
> @@ -117,8 +116,23 @@ static void panthor_hw_info_init(struct panthor_device *ptdev)
>  		 ptdev->gpu_info.tiler_present);
>  }
>  
> +static int panthor_hw_gpu_id_init(struct panthor_device *ptdev)
> +{
> +	ptdev->gpu_info.gpu_id = gpu_read(ptdev, GPU_ID);
> +	if (!ptdev->gpu_info.gpu_id)
> +		return -ENXIO;
> +
> +	return 0;
> +}
> +
>  int panthor_hw_init(struct panthor_device *ptdev)
>  {
> +	int ret = 0;
> +
> +	ret = panthor_hw_gpu_id_init(ptdev);
> +	if (ret)
> +		return ret;
> +
>  	panthor_hw_info_init(ptdev);
>  
>  	return 0;