On Fri, Oct 13, 2023 at 02:28:21PM +0200, Nirmoy Das wrote:
> Hi Ville,
>
> On 10/13/2023 12:50 PM, Ville Syrjälä wrote:
> > On Fri, Oct 13, 2023 at 12:31:40PM +0200, Nirmoy Das wrote:
> >> gen8_ggtt_invalidate() is only needed for limitted set of platforms
> >> where GGTT is mapped as WC
> > I know there is supposed to be some kind hw snooping of the ggtt
> > pte writes to invalidate the tlb, but are we sure GFX_FLSH_CNTL
> > has no other side effects we depend on?
>
> I spent some time searching through the gfxspec. This GFX_FLSH_CNTL
> register only seems to be for
>
> invalidating TLB for GUnit and (from git log ) we started to do that to
> enable WC based GGTT updates.
>
>
> So if I am not missing anything obvious then this should be safe.
OK.
The only code related complaint I have is that you are now duplicating
that same platform check in two different places. It's always better to
have a single point of truth instead of two or more, so that there is
no risk of introducing bugs due to mismatches.
>
>
> Regards,
>
> Nirmoy
>
> >
> >> otherwise this can cause unwanted
> >> side-effects on XE_HP platforms where GFX_FLSH_CNTL_GEN6 is not
> >> valid.
> >>
> >> Fixes: d2eae8e98d59 ("drm/i915/dg2: Drop force_probe requirement")
> >> Cc: Rodrigo Vivi <[email protected]>
> >> Cc: Tvrtko Ursulin <[email protected]>
> >> Cc: Joonas Lahtinen <[email protected]>
> >> Cc: Jani Nikula <[email protected]>
> >> Cc: Jonathan Cavitt <[email protected]>
> >> Cc: John Harrison <[email protected]>
> >> Cc: Andi Shyti <[email protected]>
> >> Cc: <[email protected]> # v6.2+
> >> Suggested-by: Matt Roper <[email protected]>
> >> Signed-off-by: Nirmoy Das <[email protected]>
> >> ---
> >> drivers/gpu/drm/i915/gt/intel_ggtt.c | 6 +++++-
> >> 1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> >> b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> >> index 4d7d88b92632..c2858d434bce 100644
> >> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> >> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> >> @@ -197,13 +197,17 @@ void gen6_ggtt_invalidate(struct i915_ggtt *ggtt)
> >>
> >> static void gen8_ggtt_invalidate(struct i915_ggtt *ggtt)
> >> {
> >> + struct drm_i915_private *i915 = ggtt->vm.i915;
> >> struct intel_uncore *uncore = ggtt->vm.gt->uncore;
> >>
> >> /*
> >> * Note that as an uncached mmio write, this will flush the
> >> * WCB of the writes into the GGTT before it triggers the invalidate.
> >> + *
> >> + * Only perform this when GGTT is mapped as WC, see ggtt_probe_common().
> >> */
> >> - intel_uncore_write_fw(uncore, GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);
> >> + if (!IS_GEN9_LP(i915) && GRAPHICS_VER(i915) < 11)
> >> + intel_uncore_write_fw(uncore, GFX_FLSH_CNTL_GEN6,
> >> GFX_FLSH_CNTL_EN);
> >> }
> >>
> >> static void guc_ggtt_invalidate(struct i915_ggtt *ggtt)
> >> --
> >> 2.41.0
--
Ville Syrjälä
Intel
