Hi
Am 24.02.25 um 15:29 schrieb andriy.shevchenko@xxxxxxxxxxxxxxx:
On Mon, Feb 24, 2025 at 01:38:32PM +0000, Aditya Garg wrote:
From: Kerem Karabay <kekrby@xxxxxxxxx>
Add XRGB8888 emulation helper for devices that only support BGR888.
...
+static void drm_fb_xrgb8888_to_bgr888_line(void *dbuf, const void *sbuf, unsigned int pixels)
Okay the xrgb8888 is the actual pixel format independently on
the CPU endianess.
+{
+ u8 *dbuf8 = dbuf;
+ const __le32 *sbuf32 = sbuf;
But here we assume that sbuf is __le32.
And I think we may benefit from the __be32 there.
No, please. XRGB is the logical order. The raw physical byte order for
DRM formats is always* little endian, hence reversed from the logical
one. sbuf points to raw memory and is therefore __le32. DRM-format byte
order is impossible to understand, I know. But that code is correct.
Best regards
Thomas
*) White lie: there's a DRM format flag signalling physical big
endianess. That isn't the case here. So nothing here should ever
indicate big endianess.
+ unsigned int x;
+ u32 pix;
+
+ for (x = 0; x < pixels; x++) {
+ pix = le32_to_cpu(sbuf32[x]);
+ /* write red-green-blue to output in little endianness */
+ *dbuf8++ = (pix & 0x00ff0000) >> 16;
+ *dbuf8++ = (pix & 0x0000ff00) >> 8;
+ *dbuf8++ = (pix & 0x000000ff) >> 0;
pix = be32_to_cpu(sbuf[4 * x]) >> 8;
put_unaligned_le24(pix, &dbuf[3 * x]);
+ }
Or, after all, this __le32 magic might be not needed at all. Wouldn't the below
be the equivalent
static void drm_fb_xrgb8888_to_bgr888_line(void *dbuf, const void *sbuf, unsigned int pixels)
{
unsigned int x;
u32 pix;
for (x = 0; x < pixels; x++) {
/* Read red-green-blue from input in big endianess and... */
pix = get_unaligned_be24(sbuf + x * 4 + 1);
/* ...write it to output in little endianness. */
put_unaligned_le24(pix, dbuf + x * 3);
}
}
The comments can even be dropped as the code quite clear about what's going on.
+}
But it's up to you. I don't know which solution gives better code generation
either.
--
--
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)
