linux-kernel - [PATCH v6 06/15] dma-buf/sync

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Date:   Fri, 24 Feb 2023 12:01:34 -0800
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Simon Ser <contact@...rsion.fr>,
        Luben Tuikov <luben.tuikov@....com>,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        linux-media@...r.kernel.org (open list:SYNC FILE FRAMEWORK),
        linaro-mm-sig@...ts.linaro.org (moderated list:DMA BUFFER SHARING
        FRAMEWORK), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v6 06/15] dma-buf/sync_file: Support (E)POLLPRI

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

Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent
wait (as opposed to a "housekeeping" wait to know when to cleanup after
some work has completed).  Usermode components of GPU driver stacks
often poll() on fence fd's to know when it is safe to do things like
free or reuse a buffer, but they can also poll() on a fence fd when
waiting to read back results from the GPU.  The EPOLLPRI/POLLPRI flag
lets the kernel differentiate these two cases.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/dma-buf/sync_file.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 418021cfb87c..cbe96295373b 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait)
 {
 	struct sync_file *sync_file = file->private_data;
 
+	/*
+	 * The POLLPRI/EPOLLPRI flag can be used to signal that
+	 * userspace wants the fence to signal ASAP, express this
+	 * as an immediate deadline.
+	 */
+	if (poll_requested_events(wait) & EPOLLPRI)
+		dma_fence_set_deadline(sync_file->fence, ktime_get());
+
 	poll_wait(file, &sync_file->wq, wait);
 
 	if (list_empty(&sync_file->cb.node) &&
-- 
2.39.1