[Intel-gfx] [PATCH 03/19] iosys-map: Add a few more helpers
Lucas De Marchi
lucas.demarchi at intel.com
Fri Feb 4 19:44:42 UTC 2022
On Fri, Feb 04, 2022 at 08:05:56PM +0100, Thomas Zimmermann wrote:
>Hi
>
>Am 04.02.22 um 18:44 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().
>>
>>Cc: Sumit Semwal <sumit.semwal at linaro.org>
>>Cc: Christian König <christian.koenig at amd.com>
>>Cc: Thomas Zimmermann <tzimmermann at suse.de>
>>Cc: dri-devel at lists.freedesktop.org
>>Cc: linux-kernel at vger.kernel.org
>>Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
>>---
>> include/linux/iosys-map.h | 154 +++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 153 insertions(+), 1 deletion(-)
>>
>>diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h
>>index edd7fa3be9e9..96f8b61ac6fb 100644
>>--- a/include/linux/iosys-map.h
>>+++ b/include/linux/iosys-map.h
>>@@ -6,6 +6,7 @@
>> #ifndef __IOSYS_MAP_H__
>> #define __IOSYS_MAP_H__
>>+#include <linux/kernel.h>
>> #include <linux/io.h>
>> #include <linux/string.h>
>>@@ -133,6 +134,45 @@ static inline void iosys_map_set_vaddr(struct iosys_map *map, void *vaddr)
>> 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
>>+ * using a uninitialized variable.
>>+ */
>>+#define IOSYS_MAP_INIT_OFFSET(map_, offset_) (struct iosys_map) \
>>+ { \
>>+ .vaddr = (map_)->vaddr + (offset_), \
>>+ .is_iomem = (map_)->is_iomem, \
>>+ }
>
>I already nak'ed this macro. This works because of the aliasing rules
>within the union and the fact that there are only plain pointers. But
>this is fragile. Do anything more complicated and it breaks. There's
>not even a test that would tell you that it failed.
>
>Therefore, struct iosys_map should only be initialized by the code
>that creates the stored pointer.
I wonder if there is an alternative that is not fragile that allows us
to have a macro like that. In that thread I and Daniel continued
chatting and after my additional explanations he was convinced about
that.
I only came up with such a macro after doing the rest of the patches and
noticing a pattern that is hard to debug otherwise. I expanded the
explanation in the doc above this macro.
Maybe something like:
#define IOSYS_MAP_INIT_OFFSET(map_, offset_) ({ \
struct iosys_map copy = *(map_); \
iosys_map_incr(©, offset_); \
copy; \
})
Hopefully the compiler elides the additional copy, but I need to check.
>
>However, you won't need the offset'ed iosys_map because the
>memcpy_to/from helpers now have the offset parameter.
I can't see how the offset would help. The idea is to use a shallow copy
of the map so another function or even compilation unit can be
designated to read/write part of the struct overlayed in the map... not
even have knowledge of the outer struct.
>
>
>
>>+
>> /**
>> * iosys_map_set_vaddr_iomem - Sets a iosys mapping structure to an address in I/O memory
>> * @map: The iosys_map structure
>>@@ -220,7 +260,7 @@ static inline void iosys_map_clear(struct iosys_map *map)
>> }
>> /**
>>- * iosys_map_memcpy_to_offset - Memcpy into offset of iosys_map
>>+ * iosys_map_memcpy_to - Memcpy into iosys_map
>
>That's the fix for the other patch. :)
yep :-/
>
>> * @dst: The iosys_map structure
>> * @dst_offset: The offset from which to copy
>> * @src: The source buffer
>>@@ -239,6 +279,26 @@ 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 +315,96 @@ 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);
>>+}
>
>I've found that memset32() and memset64() can significantly faster. If
>ever needed, we can add variants here as well.
>
>>+
>>+/**
>>+ * 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_type__: The struct describing the layout of the mapping
>>+ * @field__: Member of the struct to read
>>+ *
>>+ * Read a value from iosys_map assuming its layout is described by a struct,
>>+ * passed as argument. The offset and size to the struct member is calculated
>>+ * and possible un-aligned accesses to the mapping handled.
>>+ *
>>+ * Returns:
>>+ * The value read from the mapping.
>>+ */
>>+#define iosys_map_rd_field(map__, struct_type__, field__) ({ \
>
>This macro should also have an offset__ parameter and forward it to
>iosys_map_rd.
offset is actually this macro helps calculating:
struct foo {
struct bla { ... };
struct bla2 { ... };
int something_else;
};
iosys_map_rd_field(&map, struct foo, bla.x);
I feel an offset to the map, where struct foo would be located, would be
redundant if you delegated a function to update, say, struct bla and
that part alone.
This pattern happens in patch "drm/i915/guc: Convert engine record to
iosys_map" if it helps as an example.
thanks
Lucas De Marchi
>
>>+ struct_type__ *s; \
>>+ iosys_map_rd(map__, 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_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 assuming its layout is described by a struct,
>>+ * passed as argument. The offset and size to the struct member is calculated
>>+ * and possible un-aligned accesses to the mapping handled.
>>+ */
>>+#define iosys_map_wr_field(map__, struct_type__, field__, val__) ({ \
>
>And this one should also have an offset__ parameter.
>
>Best regards
>Thomas
>
>>+ struct_type__ *s; \
>>+ iosys_map_wr(map__, 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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