Re: [PATCH v2 5/5] fbdev: Define framebuffer I/O from Linux' I/O functions

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Hi Robin, Geert

Am 28.04.23 um 14:27 schrieb Geert Uytterhoeven:
On Fri, Apr 28, 2023 at 2:18 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
On 2023-04-28 10:27, Thomas Zimmermann wrote:
Implement framebuffer I/O helpers, such as fb_read*() and fb_write*()
with Linux' regular I/O functions. Remove all ifdef cases for the
various architectures.

Most of the supported architectures use __raw_() I/O functions or treat
framebuffer memory like regular memory. This is also implemented by the
architectures' I/O function, so we can use them instead.

Sparc uses SBus to connect to framebuffer devices. It provides respective
implementations of the framebuffer I/O helpers. The involved sbus_()
I/O helpers map to the same code as Sparc's regular I/O functions. As
with other platforms, we can use those instead.

We leave a TODO item to replace all fb_() functions with their regular
I/O counterparts throughout the fbdev drivers.

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
---
   include/linux/fb.h | 63 +++++++++++-----------------------------------
   1 file changed, 15 insertions(+), 48 deletions(-)

diff --git a/include/linux/fb.h b/include/linux/fb.h
index 08cb47da71f8..4aa9e90edd17 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -15,7 +15,6 @@
   #include <linux/list.h>
   #include <linux/backlight.h>
   #include <linux/slab.h>
-#include <asm/io.h>

   struct vm_area_struct;
   struct fb_info;
@@ -511,58 +510,26 @@ struct fb_info {
    */
   #define STUPID_ACCELF_TEXT_SHIT

-// This will go away
-#if defined(__sparc__)
-
-/* We map all of our framebuffers such that big-endian accesses
- * are what we want, so the following is sufficient.
+/*
+ * TODO: Update fbdev drivers to call the I/O helpers directly and
+ *       remove the fb_() tokens.
    */
-
-// This will go away
-#define fb_readb sbus_readb
-#define fb_readw sbus_readw
-#define fb_readl sbus_readl
-#define fb_readq sbus_readq
-#define fb_writeb sbus_writeb
-#define fb_writew sbus_writew
-#define fb_writel sbus_writel
-#define fb_writeq sbus_writeq
-#define fb_memset sbus_memset_io
-#define fb_memcpy_fromfb sbus_memcpy_fromio
-#define fb_memcpy_tofb sbus_memcpy_toio
-
-#elif defined(__i386__) || defined(__alpha__) || defined(__x86_64__) ||      \
-     defined(__hppa__) || defined(__sh__) || defined(__powerpc__) || \
-     defined(__arm__) || defined(__aarch64__) || defined(__mips__)
-
-#define fb_readb __raw_readb
-#define fb_readw __raw_readw
-#define fb_readl __raw_readl
-#define fb_readq __raw_readq
-#define fb_writeb __raw_writeb
-#define fb_writew __raw_writew
-#define fb_writel __raw_writel
-#define fb_writeq __raw_writeq

Note that on at least some architectures, the __raw variants are
native-endian, whereas the regular accessors are explicitly
little-endian, so there is a slight risk of inadvertently changing
behaviour on big-endian systems (MIPS most likely, but a few old ARM
platforms run BE as well).

Also on m68k, when ISA or PCI are enabled.

In addition, the non-raw variants may do some extras to guarantee
ordering, which you do not need on a frame buffer.

So I'd go for the __raw_*() variants everywhere.

Ok, makes sense. But it also means that we won't be able to remove the fb_() helpers. If we go with this proposal, I'll add your comments to the header file, so it's clear why they're still there.

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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