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Date:   Sat, 19 Feb 2022 20:28:26 -0800
From:   Lucas De Marchi <>
To:     Thomas Zimmermann <>
        Matthew Brost <>,
        Thomas Hellström 
        Matt Atwood <>,,
        Sumit Semwal <>,
        Daniele Ceraolo Spurio <>,
        Mauro Carvalho Chehab <>,
        Christian König <>,
        John Harrison <>
Subject: Re: [PATCH v3 02/16] iosys-map: Add a few more helpers

On Thu, Feb 17, 2022 at 09:42:08AM +0100, Thomas Zimmermann wrote:
>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().
>>   - 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
>>   - Drop kernel.h include as it's not needed anymore
>>Cc: Sumit Semwal <>
>>Cc: Christian König <>
>>Cc: Thomas Zimmermann <>
>>Cc: Mauro Carvalho Chehab <>
>>Signed-off-by: Lucas De Marchi <>
>>Reviewed-by: Mauro Carvalho Chehab <>
>>Reviewed-by: Matt Atwood <>
>Reviewed-by: Thomas Zimmermann <>

Thanks. I applied the first 2 patches to drm-intel-next.

The rest can't be applied as there are conflicts between drm-intel-next
and drm-intel-gt-next. I should have merged the rename to
drm-intel-gt-next since the guc patches need to be applied there.
I guess the rest will have to wait some tree propagation.

Lucas De Marchi

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