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.ko... 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 f2975a1525bee..2796fea70a427 100644 --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c @@ -327,6 +327,7 @@ 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"); @@ -341,6 +342,7 @@ 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); }