drm/sun4i: Enable the output on the pins (tcon0)

I noticed that with 4.16-rc1 LVDS output on A83T based TBS A711 tablet doesn't
work (there's output but it's garbled). I compared some older patches for LVDS
support with the mainlined ones and this change is missing from mainline Linux.

I don't know what the register does exactly and the harcoded register value
doesn't inspire much confidence that it will work in a general case, so I'm
sending this RFC.

This patch fixes the issue on A83T.

Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180222161217.23904-1-megous@megous.com

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 3c15cf2..51740dd 100644 (file)
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -335,6 +335,9 @@ static void sun4i_tcon0_mode_set_lvds(struct sun4i_tcon *tcon,
        regmap_update_bits(tcon->regs, SUN4I_TCON_GCTL_REG,
                           SUN4I_TCON_GCTL_IOMAP_MASK,
                           SUN4I_TCON_GCTL_IOMAP_TCON0);
+
+       /* Enable the output on the pins */
+       regmap_write(tcon->regs, SUN4I_TCON0_IO_TRI_REG, 0xe0000000);
 }
 
 static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,