Re: [PATCH v2 3/4] drm/panthor: Implement reading shader_present from nvmem

[Liviu Dudau <liviu.dudau@arm.com>]

On Sat, Dec 20, 2025 at 07:49:54PM +0100, Nicolas Frattaroli wrote:
> On some platforms, notably MediaTek MT8196, the shader_present bitmask
> in the Mali GPU register for it has cores enabled that may be faulty.
> The true shader_present bitmask is found in an efuse instead.
> 
> Implement reading shader_present from an nvmem cell if one is present,
> falling back to the Mali register if it's absent. The error codes are
> trickled up through to the probe function so that probe deferral works.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Best regards,
Liviu

> ---
>  drivers/gpu/drm/panthor/panthor_hw.c | 36 ++++++++++++++++++++++++++++++------
>  1 file changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
> index 87ebb7ae42c4..80c521784cd3 100644
> --- a/drivers/gpu/drm/panthor/panthor_hw.c
> +++ b/drivers/gpu/drm/panthor/panthor_hw.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0 or MIT
>  /* Copyright 2025 ARM Limited. All rights reserved. */
>  
> +#include <linux/nvmem-consumer.h>
>  #include <drm/drm_print.h>
>  
>  #include "panthor_device.h"
> @@ -109,7 +110,25 @@ static char *get_gpu_model_name(struct panthor_device *ptdev)
>  	return "(Unknown Mali GPU)";
>  }
>  
> -static void panthor_gpu_info_init(struct panthor_device *ptdev)
> +static int overload_shader_present(struct panthor_device *ptdev)
> +{
> +	u64 contents;
> +	int ret;
> +
> +	ret = nvmem_cell_read_variable_le_u64(ptdev->base.dev, "shader-present",
> +					      &contents);
> +	if (!ret)
> +		ptdev->gpu_info.shader_present = contents;
> +	else if (ret == -ENOENT)
> +		return 0;
> +	else
> +		return dev_err_probe(ptdev->base.dev, ret,
> +				     "Failed to read shader-present nvmem cell\n");
> +
> +	return 0;
> +}
> +
> +static int panthor_gpu_info_init(struct panthor_device *ptdev)
>  {
>  	unsigned int i;
>  
> @@ -143,13 +162,18 @@ static void panthor_gpu_info_init(struct panthor_device *ptdev)
>  		ptdev->gpu_info.tiler_present = gpu_read64(ptdev, GPU_TILER_PRESENT);
>  		ptdev->gpu_info.l2_present = gpu_read64(ptdev, GPU_L2_PRESENT);
>  	}
> +
> +	return overload_shader_present(ptdev);
>  }
>  
> -static void panthor_hw_info_init(struct panthor_device *ptdev)
> +static int panthor_hw_info_init(struct panthor_device *ptdev)
>  {
>  	u32 major, minor, status;
> +	int ret;
>  
> -	panthor_gpu_info_init(ptdev);
> +	ret = panthor_gpu_info_init(ptdev);
> +	if (ret)
> +		return ret;
>  
>  	major = GPU_VER_MAJOR(ptdev->gpu_info.gpu_id);
>  	minor = GPU_VER_MINOR(ptdev->gpu_info.gpu_id);
> @@ -172,6 +196,8 @@ static void panthor_hw_info_init(struct panthor_device *ptdev)
>  		 "shader_present=0x%0llx l2_present=0x%0llx tiler_present=0x%0llx",
>  		 ptdev->gpu_info.shader_present, ptdev->gpu_info.l2_present,
>  		 ptdev->gpu_info.tiler_present);
> +
> +	return 0;
>  }
>  
>  static int panthor_hw_bind_device(struct panthor_device *ptdev)
> @@ -218,7 +244,5 @@ int panthor_hw_init(struct panthor_device *ptdev)
>  	if (ret)
>  		return ret;
>  
> -	panthor_hw_info_init(ptdev);
> -
> -	return 0;
> +	return panthor_hw_info_init(ptdev);
>  }
> 
> -- 
> 2.52.0
>