[PATCH v3] drm/i915: Flush WC GGTT only on required platforms

[Nirmoy Das]

On 10/18/2023 3:00 PM, Andi Shyti wrote:
> Hi Nirmoy,
>
>>>> gen8_ggtt_invalidate() is only needed for limited set of platforms
>>>> where GGTT is mapped as WC. This was added as way to fix WC based GGTT in
>>>> commit 0f9b91c754b7 ("drm/i915: flush system agent TLBs on SNB") and
>>>> there are no reference in HW docs that forces us to use this on non-WC
>>>> backed GGTT.
>>>>
>>>> This can also cause unwanted side-effects on XE_HP platforms where
>>>> GFX_FLSH_CNTL_GEN6 is not valid anymore.
>>>>
>>>> v2: Add a func to detect wc ggtt detection (Ville)
>>>> v3: Improve commit log and add reference commit (Daniel)
>>>>
>>>> Fixes: d2eae8e98d59 ("drm/i915/dg2: Drop force_probe requirement")
>>> I'm wondering if this is the right Fixes, though. Should this
>>> rather be:
>>>
>>> Fixes: 6266992cf105 ("drm/i915/gt: remove GRAPHICS_VER == 10")
>> Hard to find a real Fixes for this. I just want to backport this to dg2
>> where we can have unwanted side-effects.
> yes, this piece of code has moved around enough so to make it
> diffuclt to track its origin.
>
> I think the one I found should be the correct one,

That just removes a graphics ver, not related to WC GGTT map or XE_HP.

>   but the dg2
> force probe removeal can also become a placeholder for DG2 fixes.

Yes, I have no better ideas too.


Regards,

Nirmoy

>
> I won't complain.
>
> Andi