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

[Lucas De Marchi]

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