linux-kernel - [RFC 0/3] dma-fence: Add a "boost" mechanism

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Date:   Wed, 19 May 2021 11:38:51 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        linaro-mm-sig@...ts.linaro.org (moderated list:DMA BUFFER SHARING
        FRAMEWORK), linux-kernel@...r.kernel.org (open list),
        linux-media@...r.kernel.org (open list:DMA BUFFER SHARING FRAMEWORK)
Subject: [RFC 0/3] dma-fence: Add a "boost" mechanism

From: Rob Clark <robdclark@...omium.org>

In some cases, like double-buffered rendering, missing vblanks can
trick the GPU into running at a lower frequence, when really we
want to be running at a higher frequency to not miss the vblanks
in the first place.

This is partially inspired by a trick i915 does, but implemented
via dma-fence for a couple of reasons:

1) To continue to be able to use the atomic helpers
2) To support cases where display and gpu are different drivers

The last patch is just proof of concept, in reality I think it
may want to be a bit more clever.  But sending this out as it
is as an RFC to get feedback.

Rob Clark (3):
  dma-fence: Add boost fence op
  drm/atomic: Call dma_fence_boost() when we've missed a vblank
  drm/msm: Wire up gpu boost

 drivers/gpu/drm/drm_atomic_helper.c | 11 +++++++++++
 drivers/gpu/drm/msm/msm_fence.c     | 10 ++++++++++
 drivers/gpu/drm/msm/msm_gpu.c       | 13 +++++++++++++
 drivers/gpu/drm/msm/msm_gpu.h       |  2 ++
 include/linux/dma-fence.h           | 26 ++++++++++++++++++++++++++
 5 files changed, 62 insertions(+)

-- 
2.30.2