[PATCH RFC] drm/sun4i: Enable the output on the pins (tcon0)

megous at megous.com megous at megous.com
Thu Feb 22 08:12:17 PST 2018

From: Ondrej Jirman <megous at megous.com>

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 at megous.com>
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 3c15cf24b503..51740ddb4b32 100644
--- 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,
+	/* 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,

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