Re: [PATCH v2 01/19] fbdev: Prepare generic architecture helpers

[Thomas Zimmermann]

Hi Geert

Am 11.04.23 um 10:08 schrieb Geert Uytterhoeven:

Hi Thomas,

On Thu, Apr 6, 2023 at 4:30 PM Thomas Zimmermann <tzimmerm...@suse.de> 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. The default mode set by
fb_pgprotect() is now writecombine, which is what most platforms
want.

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>.

v2:
         *  use writecombine mappings by default (Arnd)

Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>

Thanks for your patch!

--- a/include/asm-generic/fb.h
+++ b/include/asm-generic/fb.h
@@ -1,13 +1,32 @@
  /* SPDX-License-Identifier: GPL-2.0 */
+
  #ifndef __ASM_GENERIC_FB_H_
  #define __ASM_GENERIC_FB_H_
-#include <linux/fb.h>

-#define fb_pgprotect(...) do {} while (0)
+/*
+ * Only include this header file from your architecture's <asm/fb.h>.
+ */
+
+#include <asm/page.h>
+
+struct fb_info;
+struct file;
+
+#ifndef fb_pgprotect
+#define fb_pgprotect fb_pgprotect
+static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
+                               unsigned long off)

Does this affect any noMMU platforms that relied on fb_pgprotect()
doing nothing before?
Perhaps the body below should be protected by "#ifdef CONFIG_MMU"?

I cannot conclusively answer this question, but I did some grep'ing ('git grep ndef | grep CONFIG_MMU'): Only the architectures in this patchset provide <asm/fb.h> but nothing anywhere uses <asm-generic/fb.h> yet. And of those architectures, only arm and m68k have !CONFIG_MMU cases. Those are handled in the rsp patches. I think we're good.

+{
+       vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);

Shouldn't this use the pgprot_val() wrapper?

Best regards
Thomas

No, I think. Grep'ing for vm_page_prot, I'm not seeing it being used in such assignments.

+}
+#endif

Gr{oetje,eeting}s,

                         Geert

--
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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