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[PATCH 5/7] mtd: provide helper to prepare buffers for DMA operations

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  [PATCH 5/7] mtd: provide helper to prepare buffers for DMA operations Boris Brezillon <boris.brezillon@free-electrons.com> - 2016-03-08 12:20 +0100
    Re: [PATCH 5/7] mtd: provide helper to prepare buffers for DMA  operations Vinod Koul <vinod.koul@intel.com> - 2016-03-08 15:20 +0100
      Re: [PATCH 5/7] mtd: provide helper to prepare buffers for DMA  operations Boris Brezillon <boris.brezillon@free-electrons.com> - 2016-03-08 15:50 +0100

#1352891 — [PATCH 5/7] 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@free-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..3c368f0 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_map_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 cc84923..11c63f1 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>
 
@@ -406,6 +407,30 @@ 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) {
-- 
2.1.4

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#1353088 — Re: [PATCH 5/7] mtd: provide helper to prepare buffers for DMA operations

On Tue, Mar 08, 2016 at 12:15:13PM +0100, Boris Brezillon wrote:
>  
> +#ifdef CONFIG_HAS_DMA

Shouldn't this be CONFIG_DMA_ENGINE as you are preparing these descriptors
for DMA transfer?

-- 
~Vinod

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#1353111 — Re: [PATCH 5/7] mtd: provide helper to prepare buffers for DMA operations

On Tue, 8 Mar 2016 19:48:53 +0530
Vinod Koul <vinod.koul@intel.com> wrote:

> On Tue, Mar 08, 2016 at 12:15:13PM +0100, Boris Brezillon wrote:
> >  
> > +#ifdef CONFIG_HAS_DMA
> 
> Shouldn't this be CONFIG_DMA_ENGINE as you are preparing these descriptors
> for DMA transfer?
> 

Nope, scatterlist users are not necessarily using a dmaengine, some IPs
are directly embedding a dedicated DMA engine, which has no driver in
drivers/dma/.

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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