drm/sun4i: Fix exclusivity of the TCON clocks

Currently the exclusivity is enabled when the rate is set by
the mode setting functions. These functions are called by
mode_set_nofb callback of drm_crc_helper. Then exclusivity
is disabled when tcon is disabled by atomic_disable
callback.

What happens is that mode_set_nofb can be called once when
mode changes, and afterwards the system can call atomic_enable
and atomic_disable multiple times without further calls to
mode_set_nofb.

This happens:

mode_set_nofb   - clk exclusivity is enabled
atomic_enable
atomic_disable  - clk exclusivity is disabled
atomic_enable
atomic_disable  - clk exclusivity is already disabled, leading to WARN
                  in clk_rate_exclusive_put

Solution is to enable exclusivity in sun4i_tcon_channel_set_status.

Signed-off-by: Ondrej Jirman <megous@megous.com>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180310110511.14697-1-megous@megous.com

drivers/gpu/drm/sun4i/sun4i_tcon.c

@@ -103,6 +103,7 @@ static void sun4i_tcon_channel_set_status(struct sun4i_tcon *tcon, int channel,
 
 	if (enabled) {
 		clk_prepare_enable(clk);
+		clk_rate_exclusive_get(clk);
 	} else {
 		clk_rate_exclusive_put(clk);
 		clk_disable_unprepare(clk);
@@ -262,7 +263,7 @@ static void sun4i_tcon0_mode_set_common(struct sun4i_tcon *tcon,
 					const struct drm_display_mode *mode)
 {
 	/* Configure the dot clock */
-	clk_set_rate_exclusive(tcon->dclk, mode->crtc_clock * 1000);
+	clk_set_rate(tcon->dclk, mode->crtc_clock * 1000);
 
 	/* Set the resolution */
 	regmap_write(tcon->regs, SUN4I_TCON0_BASIC0_REG,
@@ -423,7 +424,7 @@ static void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
 	WARN_ON(!tcon->quirks->has_channel_1);
 
 	/* Configure the dot clock */
-	clk_set_rate_exclusive(tcon->sclk1, mode->crtc_clock * 1000);
+	clk_set_rate(tcon->sclk1, mode->crtc_clock * 1000);
 
 	/* Adjust clock delay */
 	clk_delay = sun4i_tcon_get_clk_delay(mode, 1);