Re: [PATCH 01/18] fbdev: Prepare generic architecture helpers

Hi

Am 05.04.23 um 17:53 schrieb Arnd Bergmann:
> On Wed, Apr 5, 2023, at 17:05, Thomas Zimmermann wrote:
>> Generic implementations of fb_pgprotect() and fb_is_primary_device()
>> have been in the source code for a long time. Prepare the header file
>> to make use of them.
>>
>> Improve the code by using an inline function for fb_pgprotect() and
>> by removing include statements.
>>
>> Symbols are protected by preprocessor guards. Architectures that
>> provide a symbol need to define a preprocessor token of the same
>> name and value. Otherwise the header file will provide a generic
>> implementation. This pattern has been taken from <asm/io.h>.
>>
>> Signed-off-by: Thomas Zimmermann <[email protected]>
> 
> Moving this into generic code is good, but I'm not sure
> about the default for fb_pgprotect():
> 
>> +
>> +#ifndef fb_pgprotect
>> +#define fb_pgprotect fb_pgprotect
>> +static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
>> +				unsigned long off)
>> +{ }
>> +#endif
> 
> I think most architectures will want the version we have on
> arc, arm, arm64, loongarch, and sh already:
> 
> static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
>                                  unsigned long off)
> {
>         vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> }
> 
> so I'd suggest making that version the default, and treating the
> empty ones (m68knommu, sparc32) as architecture specific
> workarounds.
> 
> I see that sparc64 and parisc use pgprot_uncached here, but as
> they don't define a custom pgprot_writecombine, this ends up being
> the same, and they can use the above definition as well.
> 
> mips defines pgprot_writecombine but uses pgprot_noncached
> in fb_pgprotect(), which is probably a mistake and should have
> been updated as part of commit 4b050ba7a66c ("MIPS: pgtable.h:
> Implement the pgprot_writecombine function for MIPS").

I would not want to change any of the other platform's functions unless 
the rsp platform maintainers ask me to.

Best regards
Thomas

> 
>      Arnd

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev