linux-kernel - Re: [PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h>

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Message-ID: <49684d58-c19d-b147-5e9f-2ac526dd50f0@suse.de>
Date:   Wed, 10 May 2023 16:27:10 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Arnd Bergmann <arnd@...db.de>, kernel test robot <lkp@...el.com>,
        Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Vineet Gupta <vgupta@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        "David S . Miller" <davem@...emloft.net>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        Sam Ravnborg <sam@...nborg.org>, suijingfeng@...ngson.cn
Cc:     oe-kbuild-all@...ts.linux.dev,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-fbdev@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-m68k@...ts.linux-m68k.org,
        loongarch@...ts.linux.dev, sparclinux@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into
 <asm/fb.h>

Hi

Am 10.05.23 um 16:15 schrieb Arnd Bergmann:
> On Wed, May 10, 2023, at 16:03, kernel test robot wrote:
> 
>>
>>     cc1: warning: arch/sh/include/mach-hp6xx: No such file or directory
>> [-Wmissing-include-dirs]
>>     cc1: warning: arch/sh/include/mach-hp6xx: No such file or directory
>> [-Wmissing-include-dirs]
>>     In file included from drivers/video/fbdev/hitfb.c:27:
>>     drivers/video/fbdev/hitfb.c: In function 'hitfb_accel_wait':
>>>> arch/sh/include/asm/hd64461.h:18:33: warning: passing argument 1 of 'fb_readw' makes pointer from integer without a cast [-Wint-conversion]
>>        18 | #define HD64461_IO_OFFSET(x)    (HD64461_IOBASE + (x))
>>           |                                 ^~~~~~~~~~~~~~~~~~~~~~
>>           |                                 |
>>           |                                 unsigned int
>>     arch/sh/include/asm/hd64461.h:93:33: note: in expansion of macro
>> 'HD64461_IO_OFFSET'
>>        93 | #define HD64461_GRCFGR          HD64461_IO_OFFSET(0x1044)
>>     /* Accelerator Configuration Register */
>>           |                                 ^~~~~~~~~~~~~~~~~
>>     drivers/video/fbdev/hitfb.c:47:25: note: in expansion of macro
>> 'HD64461_GRCFGR'
>>        47 |         while (fb_readw(HD64461_GRCFGR) &
>> HD64461_GRCFGR_ACCSTATUS) ;
> 
> I think that's a preexisting bug and I have no idea what the
> correct solution is. Looking for HD64461 shows it being used
> both with inw/outw and readw/writew, so there is no way to have
> the correct type. The sh __raw_readw() definition hides this bug,
> but that is a problem with arch/sh and it probably hides others
> as well.

The constant HD64461_IOBASE is defined as integer at

 
https://elixir.bootlin.com/linux/latest/source/arch/sh/include/asm/hd64461.h#L17

but fb_readw() expects a volatile-void pointer. I guess we could add a 
cast somewhere to silence the problem. In the current upstream code, 
that appears to be done by sh's __raw_readw() internally:

 
https://elixir.bootlin.com/linux/latest/source/arch/sh/include/asm/io.h#L35

Best regards
Thomas

> 
>         Arnd

-- 
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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