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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> Reviewed-by: Christian König <christian.koenig@amd.com> Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com> Link: https://lore.kernel.org/r/20250630143537.309052-1-tzimmermann@suse.de
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.