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d="scan'208";a="76270135" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Nov 2025 02:38:13 -0800 X-CSE-ConnectionGUID: 0FzUCnuZTWC9x35V0/Pj1g== X-CSE-MsgGUID: N7zDuTyBSiyQNna+/YVpVg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,293,1754982000"; d="scan'208";a="189361329" Received: from black.igk.intel.com ([10.91.253.5]) by fmviesa010.fm.intel.com with ESMTP; 10 Nov 2025 02:38:08 -0800 Received: by black.igk.intel.com (Postfix, from userid 1003) id 699E696; Mon, 10 Nov 2025 11:38:07 +0100 (CET) From: Andy Shevchenko To: Andy Shevchenko , Stefan Wahren , Vinod Koul , Thomas Andreatta , Caleb Sander Mateos , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org Cc: Olivier Dautricourt , Stefan Roese , Florian Fainelli , Broadcom internal kernel review list , Ray Jui , Scott Branden , Lars-Peter Clausen , Eugeniy Paltsev , Daniel Mack , Haojian Zhuang , Robert Jarzmik , Lizhi Hou , Brian Xu , Raj Kumar Rampelli , Michal Simek , Andrew Morton Subject: [PATCH v2 01/13] scatterlist: introduce sg_nents_for_dma() helper Date: Mon, 10 Nov 2025 11:23:28 +0100 Message-ID: <20251110103805.3562136-2-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20251110103805.3562136-1-andriy.shevchenko@linux.intel.com> References: <20251110103805.3562136-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251110_094249_899888_46F93514 X-CRM114-Status: GOOD ( 12.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Sometimes the user needs to split each entry on the mapped scatter list due to DMA length constrains. This helper returns a number of entities assuming that each of them is not bigger than supplied maximum length. Signed-off-by: Andy Shevchenko --- include/linux/scatterlist.h | 2 ++ lib/scatterlist.c | 25 +++++++++++++++++++++++++ 2 files changed, 27 insertions(+) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 29f6ceb98d74..6de1a2434299 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -441,6 +441,8 @@ static inline void sg_init_marker(struct scatterlist *sgl, int sg_nents(struct scatterlist *sg); int sg_nents_for_len(struct scatterlist *sg, u64 len); +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len); + struct scatterlist *sg_last(struct scatterlist *s, unsigned int); void sg_init_table(struct scatterlist *, unsigned int); void sg_init_one(struct scatterlist *, const void *, unsigned int); diff --git a/lib/scatterlist.c b/lib/scatterlist.c index 4af1c8b0775a..4d1a010f863c 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -64,6 +64,31 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len) } EXPORT_SYMBOL(sg_nents_for_len); +/** + * sg_nents_for_dma - return the count of DMA-capable entries in scatterlist + * @sgl: The scatterlist + * @sglen: The current number of entries + * @len: The maximum length of DMA-capable block + * + * Description: + * Determines the number of entries in @sgl which would be permitted in + * DMA-capable transfer if list had been split accordingly, taking into + * account chaining as well. + * + * Returns: + * the number of sgl entries needed + * + **/ +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len) +{ + struct scatterlist *sg; + int i, nents = 0; + + for_each_sg(sgl, sg, sglen, i) + nents += DIV_ROUND_UP(sg_dma_len(sg), len); + return nents; +} + /** * sg_last - return the last scatterlist entry in a list * @sgl: First entry in the scatterlist -- 2.50.1