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@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

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 0420f5c978b9..cf45d0f940f9 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -761,6 +761,7 @@ 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");
@@ -775,6 +776,7 @@ 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);
 }