On 27/01/2022 09:37, Thomas Hellström (Intel) wrote:
On 1/26/22 18:11, Robert Beckett wrote:
On 26/01/2022 13:49, Thomas Hellström (Intel) wrote:
On 1/25/22 20:35, Robert Beckett wrote:
From: Ramalingam C ramalingam.c@intel.com
Add a new platform flag, needs_compact_pt, to mark the requirement of compact pt layout support for the ppGTT when using 64K GTT pages.
With this flag has_64k_pages will only indicate requirement of 64K GTT page sizes or larger for device local memory access.
Suggested-by: Matthew Auld matthew.auld@intel.com Signed-off-by: Ramalingam C ramalingam.c@intel.com Signed-off-by: Robert Beckett bob.beckett@collabora.com
drivers/gpu/drm/i915/i915_drv.h | 10 +++++++--- drivers/gpu/drm/i915/i915_pci.c | 2 ++ drivers/gpu/drm/i915/intel_device_info.h | 1 + 3 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 44c1f98144b4..1258b7779705 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -1512,12 +1512,16 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915, /* * Set this flag, when platform requires 64K GTT page sizes or larger for
- device local memory access. Also this flag implies that we
require or
- at least support the compact PT layout for the ppGTT when using
the 64K
- GTT pages.
Why do we remove these comment lines?
Because HAS_64K_PAGES now means just 64K page, it no longer means also requires compact pt. This is to support other products that will have 64K but not have the PDE non-sharing restriction in future.
Those lines moved to the next change NEEDS_COMPACT_PT, which is now separate.
Yes, NEEDS_COMPACT_PT indicates that compact is *required* but does "HAS_64K_PAGES" still mean compact is supported? That information is lost.
Not any more. I discussed the ambiguity of the original wording with mauld on irc. We came to the conclusion that HAS_64K_PAGES should mean just that, that the hw has support for 64K pages, and says nothing about compact-pt at all.
NEEDS_COMPACT_PT means that the hw has compact-pt support and the driver is required to use it as it is a hw limitation.
There will be other devices that can support compact-pt but do not mandate its use. In this case, the current code would not use them, but there is potential for some future opportunistic use of that in the driver if desired (currently expected to include accelerated move/clear). If any opportunistic use is added to the driver, a new flag can be added along with the code that uses it to indicate compact-pt availability that is not mandatory (HAS_COMPACT_PT most likely), but as there is no code requiring it currently it should not be added yet, and the comments left as this patch does.
/Thomas