Messages in this thread Patch in this message | | | Date | Fri, 4 Feb 2022 11:44:42 -0800 | From | Lucas De Marchi <> | Subject | Re: [PATCH 03/19] iosys-map: Add a few more helpers |
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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@linaro.org> >>Cc: Christian König <christian.koenig@amd.com> >>Cc: Thomas Zimmermann <tzimmermann@suse.de> >>Cc: dri-devel@lists.freedesktop.org >>Cc: linux-kernel@vger.kernel.org >>Signed-off-by: Lucas De Marchi <lucas.demarchi@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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