linux-kernel - [PATCH] drm/sun4i: tcon: Prepare and enable TCON channel 0 clock at init

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Message-Id: <20190131132550.26355-1-paul.kocialkowski@bootlin.com>
Date:   Thu, 31 Jan 2019 14:25:50 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: [PATCH] drm/sun4i: tcon: Prepare and enable TCON channel 0 clock at init

When initializing clocks, a reference to the TCON channel 0 clock is
obtained. However, the clock is never prepared and enabled later.
Switching from simplefb to DRM actually disables the clock (that was
usually configured by U-Boot) because of that.

On the V3s, this results in a hang when writing to some mixer registers
when switching over to DRM from simplefb.

Fix this by preparing and enabling the clock when initializing other
clocks. Waiting for sun4i_tcon_channel_enable to enable the clock is
apparently too late and results in the same mixer register access hang.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
---
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index e987615c16f1..b31f5d95cadb 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -371,6 +371,7 @@ static int sun4i_tcon_init_clocks(struct device *dev,
 		dev_err(dev, "Couldn't get the TCON channel 0 clock\n");
 		return PTR_ERR(tcon->sclk0);
 	}
+	clk_prepare_enable(tcon->sclk0);
 
 	if (tcon->quirks->has_channel_1) {
 		tcon->sclk1 = devm_clk_get(dev, "tcon-ch1");
@@ -385,6 +386,7 @@ static int sun4i_tcon_init_clocks(struct device *dev,
 
 static void sun4i_tcon_free_clocks(struct sun4i_tcon *tcon)
 {
+	clk_disable_unprepare(tcon->sclk0);
 	clk_disable_unprepare(tcon->clk);
 }
 
-- 
2.20.1