Re: [PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h>

From: Thomas Zimmermann
Date: Wed May 10 2023 - 11:11:35 EST

Hi Geert

Am 10.05.23 um 16:34 schrieb Geert Uytterhoeven:
Hi Thomas,

On Wed, May 10, 2023 at 4:20 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
Am 10.05.23 um 14:34 schrieb Geert Uytterhoeven:
On Wed, May 10, 2023 at 1:06 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
Implement framebuffer I/O helpers, such as fb_read*() and fb_write*(),
in the architecture's <asm/fb.h> header file or the generic one.

The common case has been the use of regular I/O functions, such as
__raw_readb() or memset_io(). A few architectures used plain system-
memory reads and writes. Sparc used helpers for its SBus.

The architectures that used special cases provide the same code in
their __raw_*() I/O helpers. So the patch replaces this code with the
__raw_*() functions and moves it to <asm-generic/fb.h> for all

* fix fb_readq()/fb_writeq() on 64-bit mips (kernel test robot)
* include <linux/io.h> in <asm-generic/fb>; fix s390 build
* ia64, loongarch, sparc64: add fb_mem*() to arch headers
to keep current semantics (Arnd)
* implement all architectures with generic helpers
* support reordering and native byte order (Geert, Arnd)

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
Tested-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>

--- a/arch/mips/include/asm/fb.h
+++ b/arch/mips/include/asm/fb.h
@@ -12,6 +12,28 @@ static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
#define fb_pgprotect fb_pgprotect

+ * MIPS doesn't define __raw_ I/O macros, so the helpers
+ * in <asm-generic/fb.h> don't generate fb_readq() and
+ * fb_write(). We have to provide them here.

MIPS does not include <asm-generic/io.h>, nor define its own

I know, that's why the TODO says to convert it to generic I/O.

__raw_readq() and __raw_writeq()...

It doesn't define those macros, but it generates function calls of the
same names. Follow the macros at

It expands to a variety of helpers, including __raw_*().

Thanks, I forgot MIPS is using these grep-unfriendly factories...

+ *
+ * TODO: Convert MIPS to generic I/O. The helpers below can
+ * then be removed.
+ */
+#ifdef CONFIG_64BIT
+static inline u64 fb_readq(const volatile void __iomem *addr)
+ return __raw_readq(addr);

... so how can this call work?

On 64-bit builds, there's __raw_readq() and __raw_writeq().

At first, I tried to do the right thing and convert MIPS to work with
<asm-generic/io.h>. But that created a ton of follow-up errors in other
headers. So for now, it's better to handle this problem in asm/fb.h.

So isn't just adding

#define __raw_readq __raw_readq
#define __raw_writeq __raw_writeq

to arch/mips/include/asm/io.h sufficient to make <asm-generic/fb.h>
do the right thing?

That works. I had a patch that adds all missing defines to MIPS' io.h. Then I went with the current fix, which is self-contained within fbdev. But I'd leave it to arch maintainers.

Best regards



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)

Attachment: OpenPGP_signature
Description: OpenPGP digital signature