[PATCH AUTOSEL 4.20 52/81] drm/sun4i: tcon: Prepare and enable TCON channel 0 clock at init

Sasha Levin
2019-02-28T15:09:56Z

From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

[ Upstream commit b14e945bda8ae227d1bf2b1837c0c4a61721cd1a ]

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@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190131132550.26355-1-paul.kocialkowski@bootlin.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 f949287d926cd..4e0562aa2cc90 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -760,6 +760,7 @@ static int sun4i_tcon_init_clocks(struct device *dev,
return PTR_ERR(tcon->sclk0);
}
}
+ clk_prepare_enable(tcon->sclk0);

if (tcon->quirks->has_channel_1) {
tcon->sclk1 = devm_clk_get(dev, "tcon-ch1");
@@ -774,6 +775,7 @@ 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);
}

--
2.19.1