Am 26.01.22 um 21:36 schrieb Lucas De Marchi:
In certain situations it's useful to be able to read or write to an
offset that is calculated by having the memory layout given by a struct
declaration. Usually we are going to read/write a u8, u16, u32 or u64.
Add a pair of macros dma_buf_map_read_field()/dma_buf_map_write_field()
to calculate the offset of a struct member and memcpy the data from/to
the dma_buf_map. We could use readb, readw, readl, readq and the write*
counterparts, however due to alignment issues this may not work on all
architectures. If alignment needs to be checked to call the right
function, it's not possible to decide at compile-time which function to
call: so just leave the decision to the memcpy function that will do
exactly that on IO memory or dereference the pointer.
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
---
include/linux/dma-buf-map.h | 81 +++++++++++++++++++++++++++++++++++++
1 file changed, 81 insertions(+)
diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h
index 19fa0b5ae5ec..65e927d9ce33 100644
--- a/include/linux/dma-buf-map.h
+++ b/include/linux/dma-buf-map.h
@@ -6,6 +6,7 @@
#ifndef __DMA_BUF_MAP_H__
#define __DMA_BUF_MAP_H__
+#include <linux/kernel.h>
#include <linux/io.h>
#include <linux/string.h>
@@ -229,6 +230,46 @@ static inline void dma_buf_map_clear(struct dma_buf_map *map)
}
}
+/**
+ * dma_buf_map_memcpy_to_offset - Memcpy into offset of dma-buf mapping
+ * @dst: The dma-buf mapping structure
+ * @offset: The offset from which to copy
+ * @src: The source buffer
+ * @len: The number of byte in src
+ *
+ * Copies data into a dma-buf mapping with an offset. The source buffer is in
+ * system memory. Depending on the buffer's location, the helper picks the
+ * correct method of accessing the memory.
+ */
+static inline void dma_buf_map_memcpy_to_offset(struct dma_buf_map *dst, size_t offset,
+ const void *src, size_t len)
+{
+ if (dst->is_iomem)
+ memcpy_toio(dst->vaddr_iomem + offset, src, len);
+ else
+ memcpy(dst->vaddr + offset, src, len);
+}
+
+/**
+ * dma_buf_map_memcpy_from_offset - Memcpy from offset of dma-buf mapping into system memory
+ * @dst: Destination in system memory
+ * @src: The dma-buf mapping structure
+ * @src: The offset from which to copy
+ * @len: The number of byte in src
+ *
+ * Copies data from a dma-buf mapping with an offset. The dest buffer is in
+ * system memory. Depending on the mapping location, the helper picks the
+ * correct method of accessing the memory.
+ */
+static inline void dma_buf_map_memcpy_from_offset(void *dst, const struct dma_buf_map *src,
+ size_t offset, size_t len)
+{
+ if (src->is_iomem)
+ memcpy_fromio(dst, src->vaddr_iomem + offset, len);
+ else
+ memcpy(dst, src->vaddr + offset, len);
+}
+
Well that's certainly a valid use case, but I suggest to change the
implementation of the existing functions to call the new ones with offset=0.
This way we only have one implementation.
/**
* dma_buf_map_memcpy_to - Memcpy into dma-buf mapping
* @dst: The dma-buf mapping structure
@@ -263,4 +304,44 @@ static inline void dma_buf_map_incr(struct dma_buf_map *map, size_t incr)
map->vaddr += incr;
}
+/**
+ * dma_buf_map_read_field - Read struct member from dma-buf mapping with
+ * arbitrary size and handling un-aligned accesses
+ *
+ * @map__: The dma-buf mapping structure
+ * @type__: The struct to be used containing the field to read
+ * @field__: Member from struct we want to read
+ *
+ * Read a value from dma-buf mapping calculating the offset and size: this assumes
+ * the dma-buf mapping is aligned with a a struct type__. A single u8, u16, u32
+ * or u64 can be read, based on the offset and size of type__.field__.
+ */
+#define dma_buf_map_read_field(map__, type__, field__) ({ \
+ type__ *t__; \
+ typeof(t__->field__) val__; \
+ dma_buf_map_memcpy_from_offset(&val__, map__, offsetof(type__, field__), \
+ sizeof(t__->field__)); \
+ val__; \
+})
+
+/**
+ * dma_buf_map_write_field - Write struct member to the dma-buf mapping with
+ * arbitrary size and handling un-aligned accesses
+ *
+ * @map__: The dma-buf mapping structure
+ * @type__: The struct to be used containing the field to write
+ * @field__: Member from struct we want to write
+ * @val__: Value to be written
+ *
+ * Write a value to the dma-buf mapping calculating the offset and size.
+ * A single u8, u16, u32 or u64 can be written based on the offset and size of
+ * type__.field__.
+ */
+#define dma_buf_map_write_field(map__, type__, field__, val__) ({ \
+ type__ *t__; \
+ typeof(t__->field__) val____ = val__; \
+ dma_buf_map_memcpy_to_offset(map__, offsetof(type__, field__), \
+ &val____, sizeof(t__->field__)); \
+})
+
Uff well that absolutely looks like overkill to me.
That's a rather special use case as far as I can see and I think we
should only have this in the common framework if more than one driver is
using it.
Regards,
Christian.
#endif /* __DMA_BUF_MAP_H__ */
