linux-kernel - Re: [Intel-gfx] [PATCH v5 1/5] drm/i915: add needs_compact

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Date:   Thu, 27 Jan 2022 10:37:49 +0100
From:   Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>
To:     Robert Beckett <bob.beckett@...labora.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Matthew Auld <matthew.auld@...el.com>
Subject: Re: [Intel-gfx] [PATCH v5 1/5] drm/i915: add needs_compact_pt flag


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@...el.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@...el.com>
>>> Signed-off-by: Ramalingam C <ramalingam.c@...el.com>
>>> Signed-off-by: Robert Beckett <bob.beckett@...labora.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.

/Thomas