drm/sun4i: hdmi: Document PAD_CTRL1 output invert bits

While debugging inverted color from the HDMI output on the A10, I
found that the lowest 3 bits were set. These were cleared on A20
boards that had normal display output. By manually toggling these
bits the mapping of the color components to these bits was found.

While these are not used anywhere, it would be nice to document
them somewhere.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171014040252.9621-7-wens@csie.org

diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi.h b/drivers/gpu/drm/sun4i/sun4i_hdmi.h
index 9b97da3..b685ee1 100644 (file)
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi.h
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi.h
@@ -72,6 +72,11 @@
 #define SUN4I_HDMI_PAD_CTRL1_HALVE_CLK         BIT(6)
 #define SUN4I_HDMI_PAD_CTRL1_REG_AMP(n)                (((n) & 7) << 3)
 
+/* These bits seem to invert the TMDS data channels */
+#define SUN4I_HDMI_PAD_CTRL1_INVERT_R          BIT(2)
+#define SUN4I_HDMI_PAD_CTRL1_INVERT_G          BIT(1)
+#define SUN4I_HDMI_PAD_CTRL1_INVERT_B          BIT(0)
+
 #define SUN4I_HDMI_PLL_CTRL_REG                0x208
 #define SUN4I_HDMI_PLL_CTRL_PLL_EN             BIT(31)
 #define SUN4I_HDMI_PLL_CTRL_BWS                        BIT(30)