[PATCH] drm/gem-shmem: Do not map s/g table by default

[PATCH] drm/gem-shmem: Do not map s/g table by default

[Thomas Zimmermann]

The vast majority of drivers that use GEM-SHMEM helpers do not use
an s/g table for imported buffers; specifically all drivers that use
DRM_GEM_SHMEM_DRIVER_OPS. Therefore convert the initializer macro
to DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT and remove the latter. This
helps to avoid swiotbl errors, such as seen with some Aspeed systems

  ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)

The error is caused by the system's limited DMA capabilities and can
happen with any GEM-SHMEM-based driver. It results in a performance
penalty.

In the case of vgem and vkms, the devices do not support DMA at all,
which can result in failure to map the buffer object into the kernel's
address space. [1][2] Avoiding the s/g table fixes this problem.

The other drivers based on GEM-SHMEM, imagination, lima, panfrost,
panthor, v3d and virtio, use the s/g table of imported buffers. Neither
driver uses the default initializer, so they won't be affected by
this change.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
Closes: https://lore.kernel.org/dri-devel/6d22bce3-4533-4cfa-96ba-64352b715741@linux.dev/ # [1]
Reported-by: José Expósito <jose.exposito89@gmail.com>
Closes: https://lore.kernel.org/dri-devel/20250311172054.2903-1-jose.exposito89@gmail.com/ # [2]
---
 drivers/gpu/drm/ast/ast_drv.c      |  2 +-
 drivers/gpu/drm/udl/udl_drv.c      |  2 +-
 include/drm/drm_gem_shmem_helper.h | 18 +++---------------
 3 files changed, 5 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_drv.c b/drivers/gpu/drm/ast/ast_drv.c
index 054acda41909..6fbf62a99c48 100644
--- a/drivers/gpu/drm/ast/ast_drv.c
+++ b/drivers/gpu/drm/ast/ast_drv.c
@@ -64,7 +64,7 @@ static const struct drm_driver ast_driver = {
 	.minor = DRIVER_MINOR,
 	.patchlevel = DRIVER_PATCHLEVEL,
 
-	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
+	DRM_GEM_SHMEM_DRIVER_OPS,
 	DRM_FBDEV_SHMEM_DRIVER_OPS,
 };
 
diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
index ce5ae7cacb90..1922988625eb 100644
--- a/drivers/gpu/drm/udl/udl_drv.c
+++ b/drivers/gpu/drm/udl/udl_drv.c
@@ -57,7 +57,7 @@ static const struct drm_driver driver = {
 
 	/* GEM hooks */
 	.fops = &udl_driver_fops,
-	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
+	DRM_GEM_SHMEM_DRIVER_OPS,
 	DRM_FBDEV_SHMEM_DRIVER_OPS,
 
 	.name = DRIVER_NAME,
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 35f7466dca84..92f5db84b9c2 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -293,23 +293,11 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
 /**
  * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
  *
- * This macro provides a shortcut for setting the shmem GEM operations in
- * the &drm_driver structure.
+ * This macro provides a shortcut for setting the shmem GEM operations
+ * in the &drm_driver structure. Drivers that do not require an s/g table
+ * for imported buffers should use this.
  */
 #define DRM_GEM_SHMEM_DRIVER_OPS \
-	.gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
-	.dumb_create		   = drm_gem_shmem_dumb_create
-
-/**
- * DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT - shmem GEM operations
- *                                       without mapping sg_table on
- *                                       imported buffer.
- *
- * This macro provides a shortcut for setting the shmem GEM operations in
- * the &drm_driver structure for drivers that do not require a sg_table on
- * imported buffers.
- */
-#define DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT \
 	.gem_prime_import       = drm_gem_shmem_prime_import_no_map, \
 	.dumb_create            = drm_gem_shmem_dumb_create
 
-- 
2.50.0

Re: [PATCH] drm/gem-shmem: Do not map s/g table by default

[Zenghui Yu]

On 2025/6/30 22:34, Thomas Zimmermann wrote:
> The vast majority of drivers that use GEM-SHMEM helpers do not use
> an s/g table for imported buffers; specifically all drivers that use
> DRM_GEM_SHMEM_DRIVER_OPS. Therefore convert the initializer macro
> to DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT and remove the latter. This
> helps to avoid swiotbl errors, such as seen with some Aspeed systems
> 
>   ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)
> 
> The error is caused by the system's limited DMA capabilities and can
> happen with any GEM-SHMEM-based driver. It results in a performance
> penalty.
> 
> In the case of vgem and vkms, the devices do not support DMA at all,
> which can result in failure to map the buffer object into the kernel's
> address space. [1][2] Avoiding the s/g table fixes this problem.
> 
> The other drivers based on GEM-SHMEM, imagination, lima, panfrost,
> panthor, v3d and virtio, use the s/g table of imported buffers. Neither
> driver uses the default initializer, so they won't be affected by
> this change.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
> Closes: https://lore.kernel.org/dri-devel/6d22bce3-4533-4cfa-96ba-64352b715741@linux.dev/ # [1]
> Reported-by: José Expósito <jose.exposito89@gmail.com>
> Closes: https://lore.kernel.org/dri-devel/20250311172054.2903-1-jose.exposito89@gmail.com/ # [2]

Tested-by: Zenghui Yu <zenghui.yu@linux.dev>

Thanks!

Re: [PATCH] drm/gem-shmem: Do not map s/g table by default

[Christian König]

On 30.06.25 16:34, Thomas Zimmermann wrote:
> The vast majority of drivers that use GEM-SHMEM helpers do not use
> an s/g table for imported buffers; specifically all drivers that use
> DRM_GEM_SHMEM_DRIVER_OPS. Therefore convert the initializer macro
> to DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT and remove the latter. This
> helps to avoid swiotbl errors, such as seen with some Aspeed systems
> 
>   ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)
> 
> The error is caused by the system's limited DMA capabilities and can
> happen with any GEM-SHMEM-based driver. It results in a performance
> penalty.
> 
> In the case of vgem and vkms, the devices do not support DMA at all,
> which can result in failure to map the buffer object into the kernel's
> address space. [1][2] Avoiding the s/g table fixes this problem.
> 
> The other drivers based on GEM-SHMEM, imagination, lima, panfrost,
> panthor, v3d and virtio, use the s/g table of imported buffers. Neither
> driver uses the default initializer, so they won't be affected by
> this change.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
> Closes: https://lore.kernel.org/dri-devel/6d22bce3-4533-4cfa-96ba-64352b715741@linux.dev/ # [1]
> Reported-by: José Expósito <jose.exposito89@gmail.com>
> Closes: https://lore.kernel.org/dri-devel/20250311172054.2903-1-jose.exposito89@gmail.com/ # [2]

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>  drivers/gpu/drm/ast/ast_drv.c      |  2 +-
>  drivers/gpu/drm/udl/udl_drv.c      |  2 +-
>  include/drm/drm_gem_shmem_helper.h | 18 +++---------------
>  3 files changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_drv.c b/drivers/gpu/drm/ast/ast_drv.c
> index 054acda41909..6fbf62a99c48 100644
> --- a/drivers/gpu/drm/ast/ast_drv.c
> +++ b/drivers/gpu/drm/ast/ast_drv.c
> @@ -64,7 +64,7 @@ static const struct drm_driver ast_driver = {
>  	.minor = DRIVER_MINOR,
>  	.patchlevel = DRIVER_PATCHLEVEL,
>  
> -	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
>  	DRM_FBDEV_SHMEM_DRIVER_OPS,
>  };
>  
> diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
> index ce5ae7cacb90..1922988625eb 100644
> --- a/drivers/gpu/drm/udl/udl_drv.c
> +++ b/drivers/gpu/drm/udl/udl_drv.c
> @@ -57,7 +57,7 @@ static const struct drm_driver driver = {
>  
>  	/* GEM hooks */
>  	.fops = &udl_driver_fops,
> -	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
>  	DRM_FBDEV_SHMEM_DRIVER_OPS,
>  
>  	.name = DRIVER_NAME,
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 35f7466dca84..92f5db84b9c2 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -293,23 +293,11 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>  /**
>   * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
>   *
> - * This macro provides a shortcut for setting the shmem GEM operations in
> - * the &drm_driver structure.
> + * This macro provides a shortcut for setting the shmem GEM operations
> + * in the &drm_driver structure. Drivers that do not require an s/g table
> + * for imported buffers should use this.
>   */
>  #define DRM_GEM_SHMEM_DRIVER_OPS \
> -	.gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
> -	.dumb_create		   = drm_gem_shmem_dumb_create
> -
> -/**
> - * DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT - shmem GEM operations
> - *                                       without mapping sg_table on
> - *                                       imported buffer.
> - *
> - * This macro provides a shortcut for setting the shmem GEM operations in
> - * the &drm_driver structure for drivers that do not require a sg_table on
> - * imported buffers.
> - */
> -#define DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT \
>  	.gem_prime_import       = drm_gem_shmem_prime_import_no_map, \
>  	.dumb_create            = drm_gem_shmem_dumb_create
>  

Re: [PATCH] drm/gem-shmem: Do not map s/g table by default

[Louis Chauvet]

Le 30/06/2025 à 16:34, Thomas Zimmermann a écrit :
> The vast majority of drivers that use GEM-SHMEM helpers do not use
> an s/g table for imported buffers; specifically all drivers that use
> DRM_GEM_SHMEM_DRIVER_OPS. Therefore convert the initializer macro
> to DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT and remove the latter. This
> helps to avoid swiotbl errors, such as seen with some Aspeed systems
> 
>    ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)
> 
> The error is caused by the system's limited DMA capabilities and can
> happen with any GEM-SHMEM-based driver. It results in a performance
> penalty.
> 
> In the case of vgem and vkms, the devices do not support DMA at all,
> which can result in failure to map the buffer object into the kernel's
> address space. [1][2] Avoiding the s/g table fixes this problem.
> 
> The other drivers based on GEM-SHMEM, imagination, lima, panfrost,
> panthor, v3d and virtio, use the s/g table of imported buffers. Neither
> driver uses the default initializer, so they won't be affected by
> this change.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>

> Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
> Closes: https://lore.kernel.org/dri-devel/6d22bce3-4533-4cfa-96ba-64352b715741@linux.dev/ # [1]
> Reported-by: José Expósito <jose.exposito89@gmail.com>
> Closes: https://lore.kernel.org/dri-devel/20250311172054.2903-1-jose.exposito89@gmail.com/ # [2]
> ---
>   drivers/gpu/drm/ast/ast_drv.c      |  2 +-
>   drivers/gpu/drm/udl/udl_drv.c      |  2 +-
>   include/drm/drm_gem_shmem_helper.h | 18 +++---------------
>   3 files changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_drv.c b/drivers/gpu/drm/ast/ast_drv.c
> index 054acda41909..6fbf62a99c48 100644
> --- a/drivers/gpu/drm/ast/ast_drv.c
> +++ b/drivers/gpu/drm/ast/ast_drv.c
> @@ -64,7 +64,7 @@ static const struct drm_driver ast_driver = {
>   	.minor = DRIVER_MINOR,
>   	.patchlevel = DRIVER_PATCHLEVEL,
>   
> -	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
>   	DRM_FBDEV_SHMEM_DRIVER_OPS,
>   };
>   
> diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
> index ce5ae7cacb90..1922988625eb 100644
> --- a/drivers/gpu/drm/udl/udl_drv.c
> +++ b/drivers/gpu/drm/udl/udl_drv.c
> @@ -57,7 +57,7 @@ static const struct drm_driver driver = {
>   
>   	/* GEM hooks */
>   	.fops = &udl_driver_fops,
> -	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
>   	DRM_FBDEV_SHMEM_DRIVER_OPS,
>   
>   	.name = DRIVER_NAME,
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 35f7466dca84..92f5db84b9c2 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -293,23 +293,11 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>   /**
>    * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
>    *
> - * This macro provides a shortcut for setting the shmem GEM operations in
> - * the &drm_driver structure.
> + * This macro provides a shortcut for setting the shmem GEM operations
> + * in the &drm_driver structure. Drivers that do not require an s/g table
> + * for imported buffers should use this.
>    */
>   #define DRM_GEM_SHMEM_DRIVER_OPS \
> -	.gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
> -	.dumb_create		   = drm_gem_shmem_dumb_create
> -
> -/**
> - * DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT - shmem GEM operations
> - *                                       without mapping sg_table on
> - *                                       imported buffer.
> - *
> - * This macro provides a shortcut for setting the shmem GEM operations in
> - * the &drm_driver structure for drivers that do not require a sg_table on
> - * imported buffers.
> - */
> -#define DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT \
>   	.gem_prime_import       = drm_gem_shmem_prime_import_no_map, \
>   	.dumb_create            = drm_gem_shmem_dumb_create
>   

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH] drm/gem-shmem: Do not map s/g table by default

[Thomas Zimmermann]

Merged

Am 30.06.25 um 16:34 schrieb Thomas Zimmermann:
> The vast majority of drivers that use GEM-SHMEM helpers do not use
> an s/g table for imported buffers; specifically all drivers that use
> DRM_GEM_SHMEM_DRIVER_OPS. Therefore convert the initializer macro
> to DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT and remove the latter. This
> helps to avoid swiotbl errors, such as seen with some Aspeed systems
>
>    ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)
>
> The error is caused by the system's limited DMA capabilities and can
> happen with any GEM-SHMEM-based driver. It results in a performance
> penalty.
>
> In the case of vgem and vkms, the devices do not support DMA at all,
> which can result in failure to map the buffer object into the kernel's
> address space. [1][2] Avoiding the s/g table fixes this problem.
>
> The other drivers based on GEM-SHMEM, imagination, lima, panfrost,
> panthor, v3d and virtio, use the s/g table of imported buffers. Neither
> driver uses the default initializer, so they won't be affected by
> this change.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
> Closes: https://lore.kernel.org/dri-devel/6d22bce3-4533-4cfa-96ba-64352b715741@linux.dev/ # [1]
> Reported-by: José Expósito <jose.exposito89@gmail.com>
> Closes: https://lore.kernel.org/dri-devel/20250311172054.2903-1-jose.exposito89@gmail.com/ # [2]
> ---
>   drivers/gpu/drm/ast/ast_drv.c      |  2 +-
>   drivers/gpu/drm/udl/udl_drv.c      |  2 +-
>   include/drm/drm_gem_shmem_helper.h | 18 +++---------------
>   3 files changed, 5 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/ast/ast_drv.c b/drivers/gpu/drm/ast/ast_drv.c
> index 054acda41909..6fbf62a99c48 100644
> --- a/drivers/gpu/drm/ast/ast_drv.c
> +++ b/drivers/gpu/drm/ast/ast_drv.c
> @@ -64,7 +64,7 @@ static const struct drm_driver ast_driver = {
>   	.minor = DRIVER_MINOR,
>   	.patchlevel = DRIVER_PATCHLEVEL,
>   
> -	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
>   	DRM_FBDEV_SHMEM_DRIVER_OPS,
>   };
>   
> diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
> index ce5ae7cacb90..1922988625eb 100644
> --- a/drivers/gpu/drm/udl/udl_drv.c
> +++ b/drivers/gpu/drm/udl/udl_drv.c
> @@ -57,7 +57,7 @@ static const struct drm_driver driver = {
>   
>   	/* GEM hooks */
>   	.fops = &udl_driver_fops,
> -	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
>   	DRM_FBDEV_SHMEM_DRIVER_OPS,
>   
>   	.name = DRIVER_NAME,
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 35f7466dca84..92f5db84b9c2 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -293,23 +293,11 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>   /**
>    * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
>    *
> - * This macro provides a shortcut for setting the shmem GEM operations in
> - * the &drm_driver structure.
> + * This macro provides a shortcut for setting the shmem GEM operations
> + * in the &drm_driver structure. Drivers that do not require an s/g table
> + * for imported buffers should use this.
>    */
>   #define DRM_GEM_SHMEM_DRIVER_OPS \
> -	.gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
> -	.dumb_create		   = drm_gem_shmem_dumb_create
> -
> -/**
> - * DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT - shmem GEM operations
> - *                                       without mapping sg_table on
> - *                                       imported buffer.
> - *
> - * This macro provides a shortcut for setting the shmem GEM operations in
> - * the &drm_driver structure for drivers that do not require a sg_table on
> - * imported buffers.
> - */
> -#define DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT \
>   	.gem_prime_import       = drm_gem_shmem_prime_import_no_map, \
>   	.dumb_create            = drm_gem_shmem_dumb_create
>   

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)