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

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Message-ID: <20220209064313.ithagwtjztcf4jfb@ldmartin-desk2>
Date:   Tue, 8 Feb 2022 22:43:13 -0800
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Matthew Brost <matthew.brost@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>, linux-kernel@...r.kernel.org,
        Daniele Ceraolo Spurio <daniele.ceraolospurio@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Christian König <christian.koenig@....com>,
        John Harrison <John.C.Harrison@...el.com>
Subject: Re: [PATCH v2 02/18] iosys-map: Add a few more helpers

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@...aro.org>
>>Cc: Christian König <christian.koenig@....com>
>>Cc: Thomas Zimmermann <tzimmermann@...e.de>
>>Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
>>Cc: dri-devel@...ts.freedesktop.org
>>Cc: linux-kernel@...r.kernel.org
>>Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
>>---
>>  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