linux-kernel - Re: [PATCH v2] drm/r128: fix build for UML

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Date:   Sun, 10 Oct 2021 13:53:24 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        linux-um@...ts.infradead.org
Subject: Re: [PATCH v2] drm/r128: fix build for UML

On 10/10/21 12:49 PM, Sam Ravnborg wrote:
> Hi Randy,
> 
> On Sun, Oct 10, 2021 at 10:29:55AM -0700, Randy Dunlap wrote:
>> Fix a build error on CONFIG_UML, which does not support (provide)
>> wbinvd(). UML can use the generic mb() instead.
>>
>> ../drivers/gpu/drm/r128/ati_pcigart.c: In function ‘drm_ati_pcigart_init’:
>> ../drivers/gpu/drm/r128/ati_pcigart.c:218:2: error: implicit declaration of function ‘wbinvd’ [-Werror=implicit-function-declaration]
>>    wbinvd();
>>    ^~~~~~
>>
>> Fixes: 68f5d3f3b654 ("um: add PCI over virtio emulation driver")
>> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
>> Cc: David Airlie <airlied@...ux.ie>
>> Cc: Daniel Vetter <daniel@...ll.ch>
>> Cc: dri-devel@...ts.freedesktop.org
>> Cc: Jeff Dike <jdike@...toit.com>
>> Cc: Richard Weinberger <richard@....at>
>> Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
>> Cc: linux-um@...ts.infradead.org
>> ---
>> v2: update Fixes: tag (thanks, Johannes)
>>
>>   drivers/gpu/drm/r128/ati_pcigart.c |    2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- linux-next-20211007.orig/drivers/gpu/drm/r128/ati_pcigart.c
>> +++ linux-next-20211007/drivers/gpu/drm/r128/ati_pcigart.c
>> @@ -215,7 +215,7 @@ int drm_ati_pcigart_init(struct drm_devi
>>   	}
>>   	ret = 0;
>>   
>> -#if defined(__i386__) || defined(__x86_64__)
>> +#if (defined(__i386__) || defined(__x86_64__)) && !defined(CONFIG_UML)
>>   	wbinvd();
>>   #else
>>   	mb();
> 
> If we look at drivers/video/fbdev/i810/i810_main.h
> then it looks like we can replace the above with a simple:
> #ifdef CONFIG_X86
> 	wbinvd();
> #else
> 	mb();
> #endif
> 
> If you think this would work could you try it out.
> It would be nicer with the simpler variant.

Hi Sam,
Good idea, thanks.

OK, I tested it, it works fine.

Will resend the patch later...

> Note: I have no clue what wbinvd() does - seems like some x86 assembler
> specific thingy.


-- 
~Randy