On Thu, May 9, 2013 at 4:44 PM, Jerome Glisse j.glisse@gmail.com wrote:
On Thu, May 9, 2013 at 3:46 PM, Andy Lutomirski luto@amacapital.net wrote:
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