drm/sun4i: tcon: Prepare and enable TCON channel 0 clock at init

BugLink: https://bugs.launchpad.net/bugs/1837813
[ 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index f4284b51bdca99a04e8eda109a4d67bf5c9fac74..c3b52af37ef8a7a4dc76b822fa81b3bef593ad91 100644 (file)
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -403,6 +403,7 @@ 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");
@@ -417,6 +418,7 @@ 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);
 }