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

Thomas Zimmermann <tzimmermann@xxxxxxx> · Wed, 5 Apr 2023 20:33:50 +0200

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 <tzimmermann@xxxxxxx>

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.

Make sense, thanks for the feedback. I'll send out an update soon.

Best regards
Thomas

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").

     Arnd

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

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