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

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Message-Id: <20180222161217.23904-1-megous@megous.com>
Date:   Thu, 22 Feb 2018 17:12:17 +0100
From:   megous@...ous.com
To:     dev@...ux-sunxi.org
Cc:     Ondrej Jirman <megous@...ous.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVERS FOR ALLWINNER
        A10),
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM/Allwinner
        sunXi SoC support), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH RFC] drm/sun4i: Enable the output on the pins (tcon0)

From: Ondrej Jirman <megous@...ous.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@...ous.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,
 			   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,
-- 
2.16.2