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drm/armada: add comments about HWC32 cursor colour format 

Add some comments about the format of the HWC32 cursor colour format.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Russell King 2018-07-01 15:46:54 +01:00
parent d0d765dec6
commit 5d32b660c8
1 changed files with 7 additions and 0 deletions
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7
drivers/gpu/drm/armada/armada_crtc.c
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@ -515,6 +515,13 @@ static void armada_load_cursor_argb(void __iomem *base, uint32_t *pix,
for (x = 0; x < width; x++, p++) {
uint32_t val = *p;
/*
* In "ARGB888" (HWC32) mode, writing to the SRAM
* requires these bits to contain:
* 31:24 = alpha 23:16 = blue 15:8 = green 7:0 = red
* So, it's actually ABGR8888. This is independent
* of the SWAPRB bits in DMA control register 0.
*/
val = (val & 0xff00ff00) |
(val & 0x000000ff) << 16 |
(val & 0x00ff0000) >> 16;