1. Patchew
  2. linux
  3. [PATCH 0/4] Make MT8196 get its Mali GPU shader_present from nvmem
  4. View patch

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

Nicolas Frattaroli posted 4 patches 2 days, 3 hours ago
[PATCH 3/4] drm/panthor: Implement reading shader_present from nvmem
Posted by Nicolas Frattaroli 2 days, 3 hours ago 
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>
---
 drivers/gpu/drm/panthor/panthor_hw.c | 63 ++++++++++++++++++++++++++++++++----
 1 file changed, 57 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
index 87ebb7ae42c4..eb44c8b108aa 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 +110,52 @@ 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)
+{
+	struct device *dev = ptdev->base.dev;
+	struct nvmem_cell *cell = nvmem_cell_get(dev, "shader-present");
+	ssize_t len;
+	void *buf;
+	int ret;
+
+	if (IS_ERR(cell)) {
+		/* On platforms without this cell, use the Mali register */
+		if (PTR_ERR(cell) == -ENOENT)
+			return 0;
+
+		return dev_err_probe(dev, PTR_ERR(cell),
+				     "Failed to get shader-present nvmem cell\n");
+	}
+
+	buf = nvmem_cell_read(cell, &len);
+	if (IS_ERR(buf)) {
+		ret = dev_err_probe(dev, PTR_ERR(buf),
+				    "Failed to read shader-present nvmem cell\n");
+		goto err_put_cell;
+	}
+
+	if (!len || len > 8) {
+		ret = dev_err_probe(dev, -EINVAL, "shader-present cell can't be length %ld\n",
+				    len);
+		goto err_free;
+	}
+
+	memcpy(&ptdev->gpu_info.shader_present, buf, len);
+
+	kfree(buf);
+	nvmem_cell_put(cell);
+
+	return 0;
+
+err_free:
+	kfree(buf);
+err_put_cell:
+	nvmem_cell_put(cell);
+
+	return ret;
+}
+
+static int panthor_gpu_info_init(struct panthor_device *ptdev)
 {
 	unsigned int i;
 
@@ -143,13 +189,18 @@ 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 +223,8 @@ 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 +271,5 @@ 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
Re: [PATCH 3/4] drm/panthor: Implement reading shader_present from nvmem
Posted by Steven Price 4 hours ago 
On 17/12/2025 17:03, 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: Steven Price <steven.price@arm.com>

[Although I really hope other vendors don't do this - the hardware is
broken!]

Although one NIT below if you respin for other reasons...

> ---
>  drivers/gpu/drm/panthor/panthor_hw.c | 63 ++++++++++++++++++++++++++++++++----
>  1 file changed, 57 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
> index 87ebb7ae42c4..eb44c8b108aa 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 +110,52 @@ 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)
> +{
> +	struct device *dev = ptdev->base.dev;
> +	struct nvmem_cell *cell = nvmem_cell_get(dev, "shader-present");
> +	ssize_t len;
> +	void *buf;
> +	int ret;
> +
> +	if (IS_ERR(cell)) {
> +		/* On platforms without this cell, use the Mali register */
> +		if (PTR_ERR(cell) == -ENOENT)
> +			return 0;
> +
> +		return dev_err_probe(dev, PTR_ERR(cell),
> +				     "Failed to get shader-present nvmem cell\n");
> +	}
> +
> +	buf = nvmem_cell_read(cell, &len);
> +	if (IS_ERR(buf)) {
> +		ret = dev_err_probe(dev, PTR_ERR(buf),
> +				    "Failed to read shader-present nvmem cell\n");
> +		goto err_put_cell;
> +	}
> +
> +	if (!len || len > 8) {
> +		ret = dev_err_probe(dev, -EINVAL, "shader-present cell can't be length %ld\n",
> +				    len);
> +		goto err_free;
> +	}
> +
> +	memcpy(&ptdev->gpu_info.shader_present, buf, len);
> +
> +	kfree(buf);
> +	nvmem_cell_put(cell);
> +
> +	return 0;
> +
> +err_free:
> +	kfree(buf);
> +err_put_cell:
> +	nvmem_cell_put(cell);
> +
> +	return ret;
> +}

Rather than repeating the clean up, you can do something like:

{
	void *buf = NULL;
	int ret = 0

	if (IS_ERR(cell)) {
		ret = dev_err_probe(...);
		goto out;
	}

	buf = nvmem_cell_read();
	if (IS_ERR(buf)) {
		ret = dev_err_probe(...);
		goto out;
	}

	if (!len || len > 8) {
		ret = dev_err_probe(...);
		goto out;
	}

	memcpy();

out:
	if (!IS_ERR(buf))
		kfree(buf);
	if (!IS_ERR(cell))
		nvmem_cell_put(cell);

	return ret;
}

That avoids mistakes when adding a new operation into the sequence. Or
you can use the fancy new cleanup helpers, but that feels overkill here.
But equally I'm ok if you leave the code as is - it's simple enough and
the conversation can be done later if we need it.

Thanks,
Steve

> +
> +static int panthor_gpu_info_init(struct panthor_device *ptdev)
>  {
>  	unsigned int i;
>  
> @@ -143,13 +189,18 @@ 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 +223,8 @@ 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 +271,5 @@ 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);
>  }
>
Re: [PATCH 3/4] drm/panthor: Implement reading shader_present from nvmem
Posted by Boris Brezillon 2 days, 2 hours ago 
On Wed, 17 Dec 2025 18:03:29 +0100
Nicolas Frattaroli <nicolas.frattaroli@collabora.com> 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: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_hw.c | 63 ++++++++++++++++++++++++++++++++----
>  1 file changed, 57 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
> index 87ebb7ae42c4..eb44c8b108aa 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 +110,52 @@ 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)
> +{
> +	struct device *dev = ptdev->base.dev;
> +	struct nvmem_cell *cell = nvmem_cell_get(dev, "shader-present");
> +	ssize_t len;
> +	void *buf;
> +	int ret;
> +
> +	if (IS_ERR(cell)) {
> +		/* On platforms without this cell, use the Mali register */
> +		if (PTR_ERR(cell) == -ENOENT)
> +			return 0;
> +
> +		return dev_err_probe(dev, PTR_ERR(cell),
> +				     "Failed to get shader-present nvmem cell\n");
> +	}
> +
> +	buf = nvmem_cell_read(cell, &len);
> +	if (IS_ERR(buf)) {
> +		ret = dev_err_probe(dev, PTR_ERR(buf),
> +				    "Failed to read shader-present nvmem cell\n");
> +		goto err_put_cell;
> +	}
> +
> +	if (!len || len > 8) {
> +		ret = dev_err_probe(dev, -EINVAL, "shader-present cell can't be length %ld\n",
> +				    len);
> +		goto err_free;
> +	}
> +
> +	memcpy(&ptdev->gpu_info.shader_present, buf, len);
> +
> +	kfree(buf);
> +	nvmem_cell_put(cell);
> +
> +	return 0;
> +
> +err_free:
> +	kfree(buf);
> +err_put_cell:
> +	nvmem_cell_put(cell);
> +
> +	return ret;
> +}
> +
> +static int panthor_gpu_info_init(struct panthor_device *ptdev)
>  {
>  	unsigned int i;
>  
> @@ -143,13 +189,18 @@ 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 +223,8 @@ 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 +271,5 @@ 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);
>  }
>

Patchew 2.1-devel-b67e4c2

© 2016 - 2025 Red Hat, Inc.