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

Thomas Zimmermann <tzimmermann@xxxxxxx> · Wed, 10 May 2023 17:11:27 +0200

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
architectures.

v6:
          * fix fb_readq()/fb_writeq() on 64-bit mips (kernel test robot)
v5:
          * include <linux/io.h> in <asm-generic/fb>; fix s390 build
v4:
          * ia64, loongarch, sparc64: add fb_mem*() to arch headers
            to keep current semantics (Arnd)
v3:
          * 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


https://elixir.bootlin.com/linux/latest/source/arch/mips/include/asm/io.h#L357

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




Gr{oetje,eeting}s,

                         Geert



--
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)

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