We've had reports about performance regressions after switching mgag200 from VRAM helpers to SHMEM helpers. SHMEM pages use writecombine caching by default, but can also use the platform's default page caching. Doing so improves the performance of I/O on the framebuffer.
Mgag200's hardware does not access framebuffer pages directly (i.e., via DMA), so enabling caching does not have an effect on consistency of the framebuffer memory or the displayed data.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 913ec479bb5c ("drm/mgag200: Replace VRAM helpers with SHMEM helpers") Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Emil Velikov emil.velikov@collabora.com Cc: Dave Airlie airlied@redhat.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Krzysztof Kozlowski krzk@kernel.org Cc: Gerd Hoffmann kraxel@redhat.com Cc: Sam Ravnborg sam@ravnborg.org Cc: Rong Chen rong.a.chen@intel.com Cc: John Donnelly john.p.donnelly@Oracle.com Link: https://lore.kernel.org/dri-devel/20200617092252.GA5279@shao2-debian/ --- drivers/gpu/drm/mgag200/mgag200_drv.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/mgag200/mgag200_drv.c b/drivers/gpu/drm/mgag200/mgag200_drv.c index e19660f4a637..7189c7745baf 100644 --- a/drivers/gpu/drm/mgag200/mgag200_drv.c +++ b/drivers/gpu/drm/mgag200/mgag200_drv.c @@ -36,6 +36,7 @@ static struct drm_driver mgag200_driver = { .major = DRIVER_MAJOR, .minor = DRIVER_MINOR, .patchlevel = DRIVER_PATCHLEVEL, + .gem_create_object = drm_gem_shmem_create_object_cached, DRM_GEM_SHMEM_DRIVER_OPS, };