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[87.176.189.159]) by smtp.gmail.com with ESMTPSA id 26-20020a170906311a00b0070e238ff66fsm3775274ejx.96.2022.07.12.06.12.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Jul 2022 06:12:03 -0700 (PDT) From: " =?utf-8?q?Christian_K=C3=B6nig?= " X-Google-Original-From: =?utf-8?q?Christian_K=C3=B6nig?= To: sumit.semwal@linaro.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, daniel@ffwll.ch, bas@basnieuwenhuizen.nl Cc: =?utf-8?q?Christian_K=C3=B6nig?= Subject: [PATCH] dma-buf/dma_resv_usage: update explicit sync documentation Date: Tue, 12 Jul 2022 15:12:01 +0200 Message-Id: <20220712131201.131475-1-christian.koenig@amd.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Make it clear that DMA_RESV_USAGE_BOOKMARK can be used for explicit synced user space submissions as well and document the rules around adding the same fence with different usages. Signed-off-by: Christian König --- include/linux/dma-resv.h | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index c8ccbc94d5d2..264e27e56dff 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -62,6 +62,11 @@ struct dma_resv_list; * For example when asking for WRITE fences then the KERNEL fences are returned * as well. Similar when asked for READ fences then both WRITE and KERNEL * fences are returned as well. + * + * Already used fences can be promoted in the sense that a fence with + * DMA_RESV_USAGE_BOOKMARK could become DMA_RESV_USAGE_READ by adding it again + * with this usage. But fences can never be degraded in the sense that a fence + * with DMA_RESV_USAGE_WRITE could become DMA_RESV_USAGE_READ. */ enum dma_resv_usage { /** @@ -98,10 +103,15 @@ enum dma_resv_usage { * @DMA_RESV_USAGE_BOOKKEEP: No implicit sync. * * This should be used by submissions which don't want to participate in - * implicit synchronization. + * any implicit synchronization. + * + * The most common case are preemption fences, page table updates, TLB + * flushes as well as explicit synced user submissions. * - * The most common case are preemption fences as well as page table - * updates and their TLB flushes. + * Explicit synced user user submissions can be promoted to + * DMA_RESV_USAGE_READ or DMA_RESV_USAGE_WRITE as needed using + * dma_buf_import_sync_file() when implicit synchronization should + * become necessary after initial adding of the fence. */ DMA_RESV_USAGE_BOOKKEEP };