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The new arch_phys_wc_add/del functions do the right thing both with and without MTRR support in the kernel. So we can drop these additional checks. David Herrmann suggest to also kill the DRIVER_USE_MTRR flag since it's now unused, which spurred me to do a bit a better audit of the affected drivers. David helped a lot in that. Quoting our mail discussion: On Wed, Jul 10, 2013 at 5:41 PM, David Herrmann <dh.herrmann@gmail.com> wrote: > On Wed, Jul 10, 2013 at 5:22 PM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote: >> On Wed, Jul 10, 2013 at 3:51 PM, David Herrmann <dh.herrmann@gmail.com> wrote: >>>> -#if __OS_HAS_MTRR >>>> -static inline int drm_core_has_MTRR(struct drm_device *dev) >>>> -{ >>>> - return drm_core_check_feature(dev, DRIVER_USE_MTRR); >>>> -} >>>> -#else >>>> -#define drm_core_has_MTRR(dev) (0) >>>> -#endif >>>> - >>> >>> That was the last user of DRIVER_USE_MTRR (apart from drivers setting >>> it in .driver_features). Any reason to keep it around? >> >> Yeah, I guess we could rip things out. Which will also force me to >> properly audit drivers for the eventual behaviour change this could >> entail (in case there's an x86 driver which did not ask for an mtrr, >> but iirc there isn't). > > david@david-mb ~/dev/kernel/linux $ for i in drivers/gpu/drm/* ; do if > test -d "$i" ; then if ! grep -q USE_MTRR -r $i ; then echo $i ; fi ; > fi ; done > drivers/gpu/drm/exynos > drivers/gpu/drm/gma500 > drivers/gpu/drm/i2c > drivers/gpu/drm/nouveau > drivers/gpu/drm/omapdrm > drivers/gpu/drm/qxl > drivers/gpu/drm/rcar-du > drivers/gpu/drm/shmobile > drivers/gpu/drm/tilcdc > drivers/gpu/drm/ttm > drivers/gpu/drm/udl > drivers/gpu/drm/vmwgfx > david@david-mb ~/dev/kernel/linux $ > > So for x86 gma500,nouveau,qxl,udl,vmwgfx don't set DRIVER_USE_MTRR. > But I cannot tell whether they break if we call arch_phys_wc_add/del, > anyway. At least nouveau seemed to work here, but it doesn't use AGP > or drm_bufs, I guess. Cool, thanks a lot for stitching together the list of drivers to look at. So for real KMS drivers it's the drives responsibility to add an mtrr if it needs one. nouvea, radeon, mgag200, i915 and vmwgfx do that already. Somehow the savage driver also ends up doing that, I have no idea why. Note that gma500 as a pure KMS driver doesn't need MTRR setup since the platforms that it supports all support PAT. So no MTRRs needed to get wc iomappings. The mtrr support in the drm core is all for legacy mappings of garts, framebuffers and registers. All legacy drivers set the USE_MTRR flag, so we're good there. All in all I think we can really just ditch this /endquote v2: Also kill DRIVER_USE_MTRR as suggested by David Herrmann v3: Rebase on top of David Herrmann's agp setup/cleanup changes. Cc: David Herrmann <dh.herrmann@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Acked-by: Andy Lutomirski <luto@amacapital.net> Reviewed-by: David Herrmann <dh.herrmann@gmail.com> Signed-off-by: Dave Airlie <airlied@redhat.com>
************************************************************
* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
************************************************************
The Direct Rendering Manager (drm) is a device-independent kernel-level
device driver that provides support for the XFree86 Direct Rendering
Infrastructure (DRI).
The DRM supports the Direct Rendering Infrastructure (DRI) in four major
ways:
1. The DRM provides synchronized access to the graphics hardware via
the use of an optimized two-tiered lock.
2. The DRM enforces the DRI security policy for access to the graphics
hardware by only allowing authenticated X11 clients access to
restricted regions of memory.
3. The DRM provides a generic DMA engine, complete with multiple
queues and the ability to detect the need for an OpenGL context
switch.
4. The DRM is extensible via the use of small device-specific modules
that rely extensively on the API exported by the DRM module.
Documentation on the DRI is available from:
http://dri.freedesktop.org/wiki/Documentation
http://sourceforge.net/project/showfiles.php?group_id=387
http://dri.sourceforge.net/doc/
For specific information about kernel-level support, see:
The Direct Rendering Manager, Kernel Support for the Direct Rendering
Infrastructure
http://dri.sourceforge.net/doc/drm_low_level.html
Hardware Locking for the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/hardware_locking_low_level.html
A Security Analysis of the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/security_low_level.html