linux-kernel - [PATCH 4/4] mtd: provide helper to prepare buffers for DMA operations

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Date:	Thu, 31 Mar 2016 14:29:44 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-mtd@...ts.infradead.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Gordon <david.s.gordon@...el.com>
Cc:	Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	dmaengine@...r.kernel.org,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-media@...r.kernel.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Richard Weinberger <richard@....at>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	linux-crypto@...r.kernel.org, Vignesh R <vigneshr@...com>,
	linux-mm@...ck.org, Joerg Roedel <joro@...tes.org>,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH 4/4] mtd: provide helper to prepare buffers for DMA operations

Some NAND controller drivers are making use of DMA to transfer data from
the controller to the buffer passed by the MTD user.
Provide a generic mtd_map/unmap_buf() implementation to avoid open coded
(and sometime erroneous) implementations.

Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
---
 drivers/mtd/mtdcore.c   | 66 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mtd/mtd.h | 25 +++++++++++++++++++
 2 files changed, 91 insertions(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 3096251..4c20f33 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -1253,6 +1253,72 @@ void *mtd_kmalloc_up_to(const struct mtd_info *mtd, size_t *size)
 }
 EXPORT_SYMBOL_GPL(mtd_kmalloc_up_to);
 
+#ifdef CONFIG_HAS_DMA
+/**
+ * mtd_map_buf - create an SG table and prepare it for DMA operations
+ *
+ * @mtd: mtd device description object pointer
+ * @dev: device handling the DMA operation
+ * @buf: buf used to create the SG table
+ * @len: length of buf
+ * @constraints: optional constraints to take into account when creating
+ *		 the SG table. Can be NULL if no specific constraints
+ *		 are required.
+ * @dir: direction of the DMA operation
+ *
+ * This function should be used when an MTD driver wants to do DMA operations
+ * on a buffer passed by the MTD layer. This functions takes care of
+ * vmallocated buffer constraints, and return and sg_table that you can safely
+ * use.
+ */
+int mtd_map_buf(struct mtd_info *mtd, struct device *dev,
+		struct sg_table *sgt, const void *buf, size_t len,
+		const struct sg_constraints *constraints,
+		enum dma_data_direction dir)
+{
+	int ret;
+
+	ret = sg_alloc_table_from_buf(sgt, buf, len, constraints, GFP_KERNEL);
+	if (ret)
+		return ret;
+
+	ret = dma_map_sg(dev, sgt->sgl, sgt->nents, dir);
+	if (!ret)
+		ret = -ENOMEM;
+
+	if (ret < 0) {
+		sg_free_table(sgt);
+		return ret;
+	}
+
+	sgt->nents = ret;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mtd_map_buf);
+
+/**
+ * mtd_unmap_buf - unmap an SG table and release its resources
+ *
+ * @mtd: mtd device description object pointer
+ * @dev: device handling the DMA operation
+ * @sgt: SG table
+ * @dir: direction of the DMA operation
+ *
+ * This function unmaps a previously mapped SG table and release SG table
+ * resources. Should be called when your DMA operation is done.
+ */
+void mtd_unmap_buf(struct mtd_info *mtd, struct device *dev,
+		   struct sg_table *sgt, enum dma_data_direction dir)
+{
+	if (sgt->orig_nents) {
+		dma_unmap_sg(dev, sgt->sgl, sgt->orig_nents, dir);
+		sg_free_table(sgt);
+	}
+}
+EXPORT_SYMBOL_GPL(mtd_unmap_buf);
+#endif /* !CONFIG_HAS_DMA */
+
 #ifdef CONFIG_PROC_FS
 
 /*====================================================================*/
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 7712721..15cff85 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -24,6 +24,7 @@
 #include <linux/uio.h>
 #include <linux/notifier.h>
 #include <linux/device.h>
+#include <linux/dma-mapping.h>
 
 #include <mtd/mtd-abi.h>
 
@@ -410,6 +411,30 @@ extern void register_mtd_user (struct mtd_notifier *new);
 extern int unregister_mtd_user (struct mtd_notifier *old);
 void *mtd_kmalloc_up_to(const struct mtd_info *mtd, size_t *size);
 
+#ifdef CONFIG_HAS_DMA
+int mtd_map_buf(struct mtd_info *mtd, struct device *dev,
+		struct sg_table *sgt, const void *buf, size_t len,
+		const struct sg_constraints *constraints,
+		enum dma_data_direction dir);
+void mtd_unmap_buf(struct mtd_info *mtd, struct device *dev,
+		   struct sg_table *sgt, enum dma_data_direction dir);
+#else
+static inline int mtd_map_buf(struct mtd_info *mtd, struct device *dev,
+			      struct sg_table *sgt, const void *buf,
+			      size_t len,
+			      const struct sg_constraints *constraints
+			      enum dma_data_direction dir)
+{
+	return -ENOTSUPP;
+}
+
+static void mtd_unmap_buf(struct mtd_info *mtd, struct device *dev,
+			  struct sg_table *sgt, enum dma_data_direction dir)
+{
+	return -ENOTSUPP;
+}
+#endif
+
 void mtd_erase_callback(struct erase_info *instr);
 
 static inline int mtd_is_bitflip(int err) {
-- 
2.5.0