Re: [PATCH v2 02/18] iosys-map: Add a few more helpers

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On Wed, Feb 09, 2022 at 07:23:04AM +0100, Thomas Zimmermann wrote:
Hi

Am 08.02.22 um 11:45 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

Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
---
 include/linux/iosys-map.h | 202 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 202 insertions(+)

diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h
index edd730b1e899..c6b223534b21 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>

Alphabetically sorted, please.

What requires kernel.h? Can this be reduced to another include statement? Maybe stddef.h for offsetof() ?

Humn... I believe it was something in the previous implementation that
is not there anymore. Because this builds fine without the include now
and I don't think it is something being included by the headers already
here.  So this additional include can just be removed.

Lucas De Marchi



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