On Thu, May 9, 2013 at 4:44 PM, Jerome Glisse [off-list ref] wrote:
On Thu, May 9, 2013 at 3:46 PM, Andy Lutomirski [off-list ref] wrote:
quoted
A fair number of drivers (mostly graphics) add write-combining MTRRs.
Most ignore errors and most add the MTRR even on PAT systems which don't
need to use MTRRs.
This comment is wrong, as i said we need MTRR on PAT system for VRAM.
I didn't follow it last time.
- If userspace is setting an MTRR directly, then it will work exactly
as before -- this patch has no effect on the userspace MTRR APIs.
- If userspace uses the drm map interface with DRM_FRAME_BUFFER or
DRM_WRITE_COMBINING, there won't be an MTRR but the range will still
be WC.
- If userspace uses GEM or TTM, then everything should still use WC
(TTM has explicit handling for this, which I presume is correct, and
i915, the major GEM user, already doesn't set an MTRR).
- If userspace does not map the range, then either the kernel driver
is buggy or it doesn't matter because there's no map.
Is there a case I've missed?
--Andy