linux-kernel - Re: [PATCH v2 5/5] fbdev: Define framebuffer I/O from Linux' I/O functions

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Date:   Fri, 28 Apr 2023 16:18:38 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     deller@....de, geert@...ux-m68k.org, javierm@...hat.com,
        daniel@...ll.ch, vgupta@...nel.org, chenhuacai@...nel.org,
        kernel@...0n.name, davem@...emloft.net,
        James.Bottomley@...senpartnership.com, arnd@...db.de,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arch@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-parisc@...r.kernel.org
Subject: Re: [PATCH v2 5/5] fbdev: Define framebuffer I/O from Linux' I/O
 functions

Hi

Am 28.04.23 um 15:12 schrieb Sam Ravnborg:
> Hi Thomas,
> 
> On Fri, Apr 28, 2023 at 11:27:11AM +0200, Thomas Zimmermann wrote:
>> Implement framebuffer I/O helpers, such as fb_read*() and fb_write*()
>> with Linux' regular I/O functions. Remove all ifdef cases for the
>> various architectures.
>>
>> Most of the supported architectures use __raw_() I/O functions or treat
>> framebuffer memory like regular memory. This is also implemented by the
>> architectures' I/O function, so we can use them instead.
>>
>> Sparc uses SBus to connect to framebuffer devices. It provides respective
>> implementations of the framebuffer I/O helpers. The involved sbus_()
>> I/O helpers map to the same code as Sparc's regular I/O functions. As
>> with other platforms, we can use those instead.
>>
>> We leave a TODO item to replace all fb_() functions with their regular
>> I/O counterparts throughout the fbdev drivers.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>
>> ---
>>   include/linux/fb.h | 63 +++++++++++-----------------------------------
>>   1 file changed, 15 insertions(+), 48 deletions(-)
>>
>> diff --git a/include/linux/fb.h b/include/linux/fb.h
>> index 08cb47da71f8..4aa9e90edd17 100644
>> --- a/include/linux/fb.h
>> +++ b/include/linux/fb.h
>> @@ -15,7 +15,6 @@
>>   #include <linux/list.h>
>>   #include <linux/backlight.h>
>>   #include <linux/slab.h>
>> -#include <asm/io.h>
>>   
>>   struct vm_area_struct;
>>   struct fb_info;
>> @@ -511,58 +510,26 @@ struct fb_info {
>>    */
>>   #define STUPID_ACCELF_TEXT_SHIT
>>   
>> -// This will go away
>> -#if defined(__sparc__)
>> -
>> -/* We map all of our framebuffers such that big-endian accesses
>> - * are what we want, so the following is sufficient.
>> +/*
>> + * TODO: Update fbdev drivers to call the I/O helpers directly and
>> + *       remove the fb_() tokens.
>>    */
> When the __raw_* variants are used, as Geert points out, then I think
> the memcpy / memset can be replaced, but the rest seems fine to keep.

I'd either want the regular I/O functions or the fb_() wrappers, but not 
the __raw_() function. I'd also prefer to keep fb_ in front of memset 
and memcpy.  I'd be happy to have fb_() wrappers that are I/O helpers 
without ordering guarantees. I'd just wouldn't want them in <linux/fb.h>

Best regards
Thomas

> 
> My personal opinion is that __raw_* is for macro use etc, and not
> something to use everywhere. So I like the fb_read/fb_write macros.
> But that is just my color of the bikeshed.
> 
> 	Sam

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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