linux-kernel - [PATCH v2 24/29] drm/sun4i: Initialize registers in tcon-top driver

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Date:   Sun,  7 Oct 2018 11:39:00 +0200
From:   Jernej Skrabec <jernej.skrabec@...l.net>
To:     maxime.ripard@...tlin.com, wens@...e.org
Cc:     robh+dt@...nel.org, sboyd@...nel.org, airlied@...ux.ie,
        architt@...eaurora.org, a.hajda@...sung.com,
        Laurent.pinchart@...asonboard.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-sunxi@...glegroups.com
Subject: [PATCH v2 24/29] drm/sun4i: Initialize registers in tcon-top driver

It turns out that TCON TOP registers in H6 SoC have non-zero reset
value. This may cause issues if bits are not changed during
configuration.

To prevent that, initialize registers to 0.

Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
---
 drivers/gpu/drm/sun4i/sun8i_tcon_top.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun8i_tcon_top.c b/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
index 3040a79f298f..37158548b447 100644
--- a/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
+++ b/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
@@ -167,6 +167,13 @@ static int sun8i_tcon_top_bind(struct device *dev, struct device *master,
 		goto err_assert_reset;
 	}
 
+	/*
+	 * At least on H6, some registers have some bits set by default
+	 * which may cause issues. Clear them here.
+	 */
+	writel(0, regs + TCON_TOP_PORT_SEL_REG);
+	writel(0, regs + TCON_TOP_GATE_SRC_REG);
+
 	/*
 	 * TCON TOP has two muxes, which select parent clock for each TCON TV
 	 * channel clock. Parent could be either TCON TV or TVE clock. For now
-- 
2.19.0