linux-kernel - Re: [PATCH v7 1/7] fbdev/hitfb: Cast I/O offset to address

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Date:   Fri, 12 May 2023 13:45:22 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     David Laight <David.Laight@...LAB.COM>,
        "deller@....de" <deller@....de>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>,
        "javierm@...hat.com" <javierm@...hat.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "vgupta@...nel.org" <vgupta@...nel.org>,
        "chenhuacai@...nel.org" <chenhuacai@...nel.org>,
        "kernel@...0n.name" <kernel@...0n.name>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "James.Bottomley@...senPartnership.com" 
        <James.Bottomley@...senPartnership.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "sam@...nborg.org" <sam@...nborg.org>,
        "suijingfeng@...ngson.cn" <suijingfeng@...ngson.cn>
Cc:     "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        kernel test robot <lkp@...el.com>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>,
        "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Artur Rojek <contact@...ur-rojek.eu>
Subject: Re: [PATCH v7 1/7] fbdev/hitfb: Cast I/O offset to address

Hi

Am 12.05.23 um 13:16 schrieb David Laight:
> From: Thomas Zimmermann
>> Sent: 12 May 2023 11:25
>>
>> Cast I/O offsets to pointers to use them with I/O functions. The I/O
>> functions expect pointers of type 'volatile void __iomem *', but the
>> offsets are plain integers. Build warnings are
>>
>>    ../drivers/video/fbdev/hitfb.c: In function 'hitfb_accel_wait':
>>    ../arch/x86/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))
>>        |                                 ^~~~~~~~~~~~~~~~~~~~~~
> ...
>>     52 | static inline u16 fb_readw(const volatile void __iomem *addr)
>>        |                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
>>
>> This patch only fixes the build warnings. It's not clear if the I/O
>> offsets can legally be passed to the I/O helpers. It was apparently
>> broken in 2007 when custom inw()/outw() helpers got removed by
>> commit 34a780a0afeb ("sh: hp6xx pata_platform support."). Fixing the
>> driver would require setting the I/O base address.
> 
> Did you try changing the definition of HD64461_IOBASE to include
> a (volatile void __iomem *) cast?

I thought about it, but didn't try it. I didn't want bend the meaning of 
OFFSET and IOBASE too much. They sound like integer constants to me.

> A lot less churn...
> 
> I'm guessing that 'sh' deosn't have in/out instructions so this
> is something that is always mapped at a fixed kernel virtual address?

No idea. I cannot try the driver and was only able to build it by 
hacking up something that makes COMPILE_TEST work.

The current patch seemed like the safest bet, even with the churn.

Best regards
Thomas

> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

-- 
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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