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[2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-4538327fed8sm37178605e9.1.2025.06.27.03.10.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Jun 2025 03:10:38 -0700 (PDT) From: Petr Tesarik To: Jonathan Corbet , Randy Dunlap , Robin Murphy , Marek Szyprowski Cc: Andrew Morton , Keith Busch , Jens Axboe , Bagas Sanjaya , linux-doc@vger.kernel.org (open list:DOCUMENTATION), linux-kernel@vger.kernel.org (open list), linux-mm@kvack.org (open list:MEMORY MANAGEMENT), Petr Tesarik Subject: [PATCH v2 8/8] docs: dma-api: clean up documentation of dma_map_sg() Date: Fri, 27 Jun 2025 12:10:15 +0200 Message-ID: <20250627101015.1600042-9-ptesarik@suse.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250627101015.1600042-1-ptesarik@suse.com> References: <20250627101015.1600042-1-ptesarik@suse.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Describe in one sentence what the function does. Do not repeat example situations when the returned number is lower than the number of segments on input. Signed-off-by: Petr Tesarik Reviewed-by: Bagas Sanjaya Tested-by: Randy Dunlap --- Documentation/core-api/dma-api.rst | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dm= a-api.rst index a075550ebbb54..6a57618118fd4 100644 --- a/Documentation/core-api/dma-api.rst +++ b/Documentation/core-api/dma-api.rst @@ -322,10 +322,10 @@ action (e.g. reduce current DMA mapping usage or dela= y and try again later). dma_map_sg(struct device *dev, struct scatterlist *sg, int nents, enum dma_data_direction direction) =20 -Returns: the number of DMA address segments mapped (this may be shorter -than passed in if some elements of the scatter/gather list are -physically or virtually adjacent and an IOMMU maps them with a single -entry). +Maps a scatter/gather list for DMA. Returns the number of DMA address segm= ents +mapped, which may be smaller than passed in if several consecutive +sglist entries are merged (e.g. with an IOMMU, or if some adjacent segments +just happen to be physically contiguous). =20 Please note that the sg cannot be mapped again if it has been mapped once. The mapping process is allowed to destroy information in the sg. @@ -349,9 +349,8 @@ With scatterlists, you use the resulting mapping like t= his:: where nents is the number of entries in the sglist. =20 The implementation is free to merge several consecutive sglist entries -into one (e.g. with an IOMMU, or if several pages just happen to be -physically contiguous) and returns the actual number of sg entries it -mapped them to. On failure 0, is returned. +into one. The returned number is the actual number of sg entries it +mapped them to. On failure, 0 is returned. =20 Then you should loop count times (note: this can be less than nents times) and use sg_dma_address() and sg_dma_len() macros where you previously --=20 2.49.0