drm/sun4i: Protect the TCON pixel clocks

Both TCON clocks are very sensitive to clock changes, since any change
might lead to improper timings.

Make sure our rate is never changed.
Tested-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d5224d2e81ecf73dc09f234e580ada52c00eaee3.1519204731.git-series.maxime.ripard@bootlin.com

drivers/gpu/drm/sun4i/sun4i_tcon.c

@@ -260,7 +260,7 @@ static void sun4i_tcon0_mode_set_common(struct sun4i_tcon *tcon,
 					const struct drm_display_mode *mode)
 {
 	/* Configure the dot clock */
-	clk_set_rate(tcon->dclk, mode->crtc_clock * 1000);
+	clk_set_rate_exclusive(tcon->dclk, mode->crtc_clock * 1000);
 
 	/* Set the resolution */
 	regmap_write(tcon->regs, SUN4I_TCON0_BASIC0_REG,
@@ -421,7 +421,7 @@ static void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
 	WARN_ON(!tcon->quirks->has_channel_1);
 
 	/* Configure the dot clock */
-	clk_set_rate(tcon->sclk1, mode->crtc_clock * 1000);
+	clk_set_rate_exclusive(tcon->sclk1, mode->crtc_clock * 1000);
 
 	/* Adjust clock delay */
 	clk_delay = sun4i_tcon_get_clk_delay(mode, 1);