On Thu, Jan 27, 2022 at 03:26:43PM +0100, Thomas Zimmermann wrote:
Hi
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);
+}
Please don't add a new function. Rather please add the offset parameter to dma_buf_map_memcpy_to() and update the callers. There are only two calls to dma_buf_map_memcpy_to() within the kernel. To make it clear what the offset applies to, I'd call the parameter 'dst_offset'.
+
+/**
+ * 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);
+}
+
With the dma_buf_map_memcpy_to() changes, please just call this function dma_buf_map_memcpy_from().
/**
* 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__)); \
+})
As the original author of this file, I feel like this shouldn't be here. At least not until we have another driver using that pattern.
Let me try to clear out the confusion. Then maybe I can extend
the documentation of this function in v2 if I'm able to convince this is
useful here.
This is not about importer/exporter, having this to work cross-driver.
This is about using dma_buf_map (which we are talking about on renaming
to iosys_map or something else) for inner driver
allocations/abstractions. The abstraction added by iosys_map helps on
sharing the same functions we had before. And this macro here is very
useful when the buffer is described by a struct layout. Example:
struct bla {
struct inner inner1;
struct inner inner2;
u32 x, y ,z;
};
Functions that would previously do:
struct bla *bla = ...;
bla->x = 100;
bla->y = 200;
bla->inner1.inner_inner_field = 30;
Can do the below, having the system/IO memory abstracted away
(calling it iosys_map here instead of dma_buf_map, hopeful it helps):
struct iosys_map *map = ...;
iosys_map_write_field(map, struct bla, x, 100);
iosys_map_write_field(map, struct bla, y, 200);
iosys_map_write_field(map, struct bla,
inner1.inner_inner_field, 30);
When we are using mostly the same map, the individual drivers can add
quick helpers on top. See the ads_blob_write() added in this series,
which guarantees the map it's working on is always the guc->ads_map,
while reducing verbosity to use the API. From patch
"drm/i915/guc: Add read/write helpers for ADS blob":
#define ads_blob_read(guc_, field_) \
dma_buf_map_read_field(&(guc_)->ads_map, struct __guc_ads_blob, \
field_)
#define ads_blob_write(guc_, field_, val_) \
dma_buf_map_write_field(&(guc_)->ads_map, struct __guc_ads_blob,\
field_, val_)
So in intel_guc_ads, we can have a lot of:
- bla->x = 100;
+ ads_blob_write(guc, x, 10);
thanks
Lucas De Marchi
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