[1/3] Provide simple noop dma ops

Commit Message

Christian Borntraeger Oct. 30, 2015, 1:20 p.m. UTC

We are going to require dma_ops for several common drivers, even for
systems that do have an identity mapping. Lets provide some minimal
no-op dma_ops that can be used for that purpose.

Signed-off-by: Christian Borntraeger <[e-mail]>
---
 include/linux/dma-mapping.h |  2 ++
 lib/Makefile                |  2 +-
 lib/dma-noop.c              | 77 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 lib/dma-noop.c

Comments

Joerg Roedel Nov. 2, 2015, 3:16 p.m. UTC | #1

On Fri, Oct 30, 2015 at 02:20:35PM +0100, Christian Borntraeger wrote:
> +static void *dma_noop_alloc(struct device *dev, size_t size,
> +			    dma_addr_t *dma_handle, gfp_t gfp,
> +			    struct dma_attrs *attrs)
> +{
> +	void *ret;
> +
> +	ret = (void *)__get_free_pages(gfp, get_order(size));
> +	if (ret) {
> +		memset(ret, 0, size);

There is no need to zero out the memory here. If the user wants
initialized memory it can call dma_zalloc_coherent. Having the memset
here means to clear the memory twice in the dma_zalloc_coherent path.

Otherwise it looks good.


	Joerg

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Christian Borntraeger Nov. 2, 2015, 4:01 p.m. UTC | #2

Am 02.11.2015 um 16:16 schrieb Joerg Roedel:
> On Fri, Oct 30, 2015 at 02:20:35PM +0100, Christian Borntraeger wrote:
>> +static void *dma_noop_alloc(struct device *dev, size_t size,
>> +			    dma_addr_t *dma_handle, gfp_t gfp,
>> +			    struct dma_attrs *attrs)
>> +{
>> +	void *ret;
>> +
>> +	ret = (void *)__get_free_pages(gfp, get_order(size));
>> +	if (ret) {
>> +		memset(ret, 0, size);
> 
> There is no need to zero out the memory here. If the user wants
> initialized memory it can call dma_zalloc_coherent. Having the memset
> here means to clear the memory twice in the dma_zalloc_coherent path.
> 
> Otherwise it looks good.

Thanks. Will fix.
In addition I will also make the compilation of dma-noop.o dependent 
on HAS_DMA.


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Patch

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index ac07ff0..7912f54 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -66,6 +66,8 @@  struct dma_map_ops {
 	int is_phys;
 };
 
+extern struct dma_map_ops dma_noop_ops;
+
 #define DMA_BIT_MASK(n)	(((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
 
 #define DMA_MASK_NONE	0x0ULL
diff --git a/lib/Makefile b/lib/Makefile
index 13a7c6a..b04ba71 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -13,7 +13,7 @@  lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 sha1.o md5.o irq_regs.o argv_split.o \
 	 proportions.o flex_proportions.o ratelimit.o show_mem.o \
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
-	 earlycpio.o seq_buf.o nmi_backtrace.o
+	 earlycpio.o seq_buf.o nmi_backtrace.o dma-noop.o
 
 obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o
 lib-$(CONFIG_MMU) += ioremap.o
diff --git a/lib/dma-noop.c b/lib/dma-noop.c
new file mode 100644
index 0000000..3ce31302
--- /dev/null
+++ b/lib/dma-noop.c
@@ -0,0 +1,77 @@ 
+/*
+ *	lib/dma-noop.c
+ *
+ * Stub DMA noop-ops
+ */
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/dma-mapping.h>
+#include <linux/scatterlist.h>
+
+static void *dma_noop_alloc(struct device *dev, size_t size,
+			    dma_addr_t *dma_handle, gfp_t gfp,
+			    struct dma_attrs *attrs)
+{
+	void *ret;
+
+	ret = (void *)__get_free_pages(gfp, get_order(size));
+	if (ret) {
+		memset(ret, 0, size);
+		*dma_handle = virt_to_phys(ret);
+	}
+	return ret;
+}
+
+static void dma_noop_free(struct device *dev, size_t size,
+			  void *cpu_addr, dma_addr_t dma_addr,
+			  struct dma_attrs *attrs)
+{
+	free_pages((unsigned long)cpu_addr, get_order(size));
+}
+
+static dma_addr_t dma_noop_map_page(struct device *dev, struct page *page,
+				      unsigned long offset, size_t size,
+				      enum dma_data_direction dir,
+				      struct dma_attrs *attrs)
+{
+	return page_to_phys(page) + offset;
+}
+
+static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
+			     enum dma_data_direction dir, struct dma_attrs *attrs)
+{
+	int i;
+	struct scatterlist *sg;
+
+	for_each_sg(sgl, sg, nents, i) {
+		void *va;
+
+		BUG_ON(!sg_page(sg));
+		va = sg_virt(sg);
+		sg_dma_address(sg) = (dma_addr_t)virt_to_phys(va);
+		sg_dma_len(sg) = sg->length;
+	}
+
+	return nents;
+}
+
+static int dma_noop_mapping_error(struct device *dev, dma_addr_t dma_addr)
+{
+	return 0;
+}
+
+static int dma_noop_supported(struct device *dev, u64 mask)
+{
+	return 1;
+}
+
+struct dma_map_ops dma_noop_ops = {
+	.alloc			= dma_noop_alloc,
+	.free			= dma_noop_free,
+	.map_page		= dma_noop_map_page,
+	.map_sg			= dma_noop_map_sg,
+	.mapping_error		= dma_noop_mapping_error,
+	.dma_supported		= dma_noop_supported,
+};
+
+EXPORT_SYMBOL(dma_noop_ops);