Re: [Intel-gfx] [PATCH v3 02/16] iosys-map: Add a few more helpers

Thomas Zimmermann
2022-02-17T08:42:18Z

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Hi

Am 16.02.22 um 18:41 schrieb Lucas De Marchi:
> First the simplest ones:
>
> - iosys_map_memset(): when abstracting system and I/O memory,
> just like the memcpy() use case, memset() also has dedicated
> functions to be called for using IO memory.
> - iosys_map_memcpy_from(): we may need to copy data from I/O
> memory, not only to.
>
> 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.
>
> As a pre-requisite for the implementation, add iosys_map_memcpy_from()
> to be the equivalent of iosys_map_memcpy_to(), but in the other
> direction. Then add 2 pairs of macros:
>
> - iosys_map_rd() / iosys_map_wr()
> - iosys_map_rd_field() / iosys_map_wr_field()
>
> The first pair takes the C-type and offset to read/write. The second
> pair uses a struct describing the layout of the mapping in order to
> calculate the offset and size being read/written.
>
> 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.
>
> Finally, in order to use the above macros with a map derived from
> another, add another initializer: IOSYS_MAP_INIT_OFFSET().
>
> v2:
> - Rework IOSYS_MAP_INIT_OFFSET() so it doesn't rely on aliasing rules
> within the union
> - Add offset to both iosys_map_rd_field() and iosys_map_wr_field() to
> allow the struct itself to be at an offset from the mapping
> - Add documentation to iosys_map_rd_field() with example and expected
> memory layout
> v3:
> - Drop kernel.h include as it's not needed anymore
>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> Cc: dri-devel@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
> Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>
> Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

> ---
> include/linux/iosys-map.h | 201 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 201 insertions(+)
>
> diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h
> index edd730b1e899..e69a002d5aa4 100644
> --- a/include/linux/iosys-map.h
> +++ b/include/linux/iosys-map.h
> @@ -120,6 +120,45 @@ struct iosys_map {
> .is_iomem = false, \
> }
>
> +/**
> + * IOSYS_MAP_INIT_OFFSET - Initializes struct iosys_map from another iosys_map
> + * @map_: The dma-buf mapping structure to copy from
> + * @offset_: Offset to add to the other mapping
> + *
> + * Initializes a new iosys_map struct based on another passed as argument. It
> + * does a shallow copy of the struct so it's possible to update the back storage
> + * without changing where the original map points to. It is the equivalent of
> + * doing:
> + *
> + * .. code-block:: c
> + *
> + * iosys_map map = other_map;
> + * iosys_map_incr(&map, &offset);
> + *
> + * Example usage:
> + *
> + * .. code-block:: c
> + *
> + * void foo(struct device *dev, struct iosys_map *base_map)
> + * {
> + * ...
> + * struct iosys_map map = IOSYS_MAP_INIT_OFFSET(base_map, FIELD_OFFSET);
> + * ...
> + * }
> + *
> + * The advantage of using the initializer over just increasing the offset with
> + * iosys_map_incr() like above is that the new map will always point to the
> + * right place of the buffer during its scope. It reduces the risk of updating
> + * the wrong part of the buffer and having no compiler warning about that. If
> + * the assignment to IOSYS_MAP_INIT_OFFSET() is forgotten, the compiler can warn
> + * about the use of uninitialized variable.
> + */
> +#define IOSYS_MAP_INIT_OFFSET(map_, offset_) ({ \
> + struct iosys_map copy = *map_; \
> + iosys_map_incr(&copy, offset_); \
> + copy; \
> +})
> +
> /**
> * iosys_map_set_vaddr - Sets a iosys mapping structure to an address in system memory
> * @map: The iosys_map structure
> @@ -239,6 +278,26 @@ static inline void iosys_map_memcpy_to(struct iosys_map *dst, size_t dst_offset,
> memcpy(dst->vaddr + dst_offset, src, len);
> }
>
> +/**
> + * iosys_map_memcpy_from - Memcpy from iosys_map into system memory
> + * @dst: Destination in system memory
> + * @src: The iosys_map structure
> + * @src_offset: The offset from which to copy
> + * @len: The number of byte in src
> + *
> + * Copies data from a iosys_map 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 iosys_map_memcpy_from(void *dst, const struct iosys_map *src,
> + size_t src_offset, size_t len)
> +{
> + if (src->is_iomem)
> + memcpy_fromio(dst, src->vaddr_iomem + src_offset, len);
> + else
> + memcpy(dst, src->vaddr + src_offset, len);
> +}
> +
> /**
> * iosys_map_incr - Increments the address stored in a iosys mapping
> * @map: The iosys_map structure
> @@ -255,4 +314,146 @@ static inline void iosys_map_incr(struct iosys_map *map, size_t incr)
> map->vaddr += incr;
> }
>
> +/**
> + * iosys_map_memset - Memset iosys_map
> + * @dst: The iosys_map structure
> + * @offset: Offset from dst where to start setting value
> + * @value: The value to set
> + * @len: The number of bytes to set in dst
> + *
> + * Set value in iosys_map. Depending on the buffer's location, the helper
> + * picks the correct method of accessing the memory.
> + */
> +static inline void iosys_map_memset(struct iosys_map *dst, size_t offset,
> + int value, size_t len)
> +{
> + if (dst->is_iomem)
> + memset_io(dst->vaddr_iomem + offset, value, len);
> + else
> + memset(dst->vaddr + offset, value, len);
> +}
> +
> +/**
> + * iosys_map_rd - Read a C-type value from the iosys_map
> + *
> + * @map__: The iosys_map structure
> + * @offset__: The offset from which to read
> + * @type__: Type of the value being read
> + *
> + * Read a C type value from iosys_map, handling possible un-aligned accesses to
> + * the mapping.
> + *
> + * Returns:
> + * The value read from the mapping.
> + */
> +#define iosys_map_rd(map__, offset__, type__) ({ \
> + type__ val; \
> + iosys_map_memcpy_from(&val, map__, offset__, sizeof(val)); \
> + val; \
> +})
> +
> +/**
> + * iosys_map_wr - Write a C-type value to the iosys_map
> + *
> + * @map__: The iosys_map structure
> + * @offset__: The offset from the mapping to write to
> + * @type__: Type of the value being written
> + * @val__: Value to write
> + *
> + * Write a C-type value to the iosys_map, handling possible un-aligned accesses
> + * to the mapping.
> + */
> +#define iosys_map_wr(map__, offset__, type__, val__) ({ \
> + type__ val = (val__); \
> + iosys_map_memcpy_to(map__, offset__, &val, sizeof(val)); \
> +})
> +
> +/**
> + * iosys_map_rd_field - Read a member from a struct in the iosys_map
> + *
> + * @map__: The iosys_map structure
> + * @struct_offset__: Offset from the beggining of the map, where the struct
> + * is located
> + * @struct_type__: The struct describing the layout of the mapping
> + * @field__: Member of the struct to read
> + *
> + * Read a value from iosys_map considering its layout is described by a C struct
> + * starting at @struct_offset__. The field offset and size is calculated and its
> + * value read handling possible un-aligned memory accesses. For example: suppose
> + * there is a @struct foo defined as below and the value ``foo.field2.inner2``
> + * needs to be read from the iosys_map:
> + *
> + * .. code-block:: c
> + *
> + * struct foo {
> + * int field1;
> + * struct {
> + * int inner1;
> + * int inner2;
> + * } field2;
> + * int field3;
> + * } __packed;
> + *
> + * This is the expected memory layout of a buffer using iosys_map_rd_field():
> + *
> + * +------------------------------+--------------------------+
> + * | Address | Content |
> + * +==============================+==========================+
> + * | buffer + 0000 | start of mmapped buffer |
> + * | | pointed by iosys_map |
> + * +------------------------------+--------------------------+
> + * | ... | ... |
> + * +------------------------------+--------------------------+
> + * | buffer + ``struct_offset__`` | start of ``struct foo`` |
> + * +------------------------------+--------------------------+
> + * | ... | ... |
> + * +------------------------------+--------------------------+
> + * | buffer + wwww | ``foo.field2.inner2`` |
> + * +------------------------------+--------------------------+
> + * | ... | ... |
> + * +------------------------------+--------------------------+
> + * | buffer + yyyy | end of ``struct foo`` |
> + * +------------------------------+--------------------------+
> + * | ... | ... |
> + * +------------------------------+--------------------------+
> + * | buffer + zzzz | end of mmaped buffer |
> + * +------------------------------+--------------------------+
> + *
> + * Values automatically calculated by this macro or not needed are denoted by
> + * wwww, yyyy and zzzz. This is the code to read that value:
> + *
> + * .. code-block:: c
> + *
> + * x = iosys_map_rd_field(&map, offset, struct foo, field2.inner2);
> + *
> + * Returns:
> + * The value read from the mapping.
> + */
> +#define iosys_map_rd_field(map__, struct_offset__, struct_type__, field__) ({ \
> + struct_type__ *s; \
> + iosys_map_rd(map__, struct_offset__ + offsetof(struct_type__, field__), \
> + typeof(s->field__)); \
> +})
> +
> +/**
> + * iosys_map_wr_field - Write to a member of a struct in the iosys_map
> + *
> + * @map__: The iosys_map structure
> + * @struct_offset__: Offset from the beggining of the map, where the struct
> + * is located
> + * @struct_type__: The struct describing the layout of the mapping
> + * @field__: Member of the struct to read
> + * @val__: Value to write
> + *
> + * Write a value to the iosys_map considering its layout is described by a C struct
> + * starting at @struct_offset__. The field offset and size is calculated and the
> + * @val__ is written handling possible un-aligned memory accesses. Refer to
> + * iosys_map_rd_field() for expected usage and memory layout.
> + */
> +#define iosys_map_wr_field(map__, struct_offset__, struct_type__, field__, val__) ({ \
> + struct_type__ *s; \
> + iosys_map_wr(map__, struct_offset__ + offsetof(struct_type__, field__), \
> + typeof(s->field__), val__); \
> +})
> +
> #endif /* __IOSYS_MAP_H__ */

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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