Hi Ville:
Thanks for the answer! :) Learned a lot.
I think the following scenario should be typical for a general PCI
devices(perhaps a dedicated video card). How do other PCI devices handle
this kinds of WC MMIO writes without GFX_FLSH_CNT? Only support UC mapping?
Thanks,
Zhi.
On 11/19/15 18:35, Ville Syrjälä wrote:
On Thu, Nov 19, 2015 at 06:20:23PM +0800, Zhi Wang wrote:
Hi Gurus:
I'm curious about the register GFX_FLSH_CNT(0x101008) in
i915_gem_gtt.c. Does these register exist in recently generations? After
digging into b-spec, it looks only BXT and CHV has this register. Does
the desktop platform also have this register which needs to be written
after updating GGTT MMIOs?
BTW: Looks windows driver haven't used this MMIO... So whose behavior is
the right behavior?
As I understand it that register flushes the CPU GTT TLBs, and we need
to do it because of the WC mapping we have for the GTT PTEs. If we used
UC mapping we wouldn't need it since there's supposedly an automagic
TLB flush that happens on PTE writes.
BSpec is bad at finding some registers via bxml. Using dtsearch and
looking for both 0x<offset> and <offset>h is the method I use to track
such things down.
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