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@xxxxxxx>
Fixes: 913ec479bb5c ("drm/mgag200: Replace VRAM helpers with SHMEM helpers")
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Emil Velikov <emil.velikov@xxxxxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Rong Chen <rong.a.chen@xxxxxxxxx>
Cc: John Donnelly <john.p.donnelly@xxxxxxxxxx>
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,
};
--
2.27.0
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