Simona Vetter simona.vetter@ffwll.ch writes:
On Wed, Dec 11, 2024 at 10:06:28AM +0100, Thomas Zimmermann wrote:
DMA areas are not necessarily backed by struct page, so we cannot rely on it for deferred I/O. Allocate a shadow buffer for drivers that require deferred I/O and use it as framebuffer memory.
Fixes driver errors about being "Unable to handle kernel NULL pointer dereference at virtual address" or "Unable to handle kernel paging request at virtual address".
The patch splits drm_fbdev_dma_driver_fbdev_probe() in an initial allocation, which creates the DMA-backed buffer object, and a tail that sets up the fbdev data structures. There is a tail function for direct memory mappings and a tail function for deferred I/O with the shadow buffer.
It is no longer possible to use deferred I/O without shadow buffer. It can be re-added if there exists a reliably test for usable struct page in the allocated DMA-backed buffer object.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reported-by: Nuno Gonçalves nunojpg@gmail.com CLoses: https://lore.kernel.org/dri-devel/CAEXMXLR55DziAMbv_+2hmLeH-jP96pmit6nhs6siB... Tested-by: Nuno Gonçalves nunojpg@gmail.com Fixes: 5ab91447aa13 ("drm/tiny/ili9225: Use fbdev-dma") Cc: Thomas Zimmermann tzimmermann@suse.de Cc: stable@vger.kernel.org # v6.11+
fbdev code scares me, but I at least tried to check a few things and looks all good.
Reviewed-by: Simona Vetter simona.vetter@ffwll.ch
Same here, is always scary to review fbdev code but the patch looks good to me.
Reviewed-by: Javier Martinez Canillas javierm@redhat.com