drm/exynos: add support for 'hdmi' clock

Mixed need to have hdmi clock enabled to properly perform power on/off
sequences, so add handling of this clock directly to the mixer driver.
Dependency between hdmi clock and mixer module has been observed on
Exynos4 based boards.

Suggested-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

Documentation/devicetree/bindings/video/exynos_mixer.txt

@@ -15,6 +15,7 @@ Required properties:
 	a) mixer: Gate of Mixer IP bus clock.
 	b) sclk_hdmi: HDMI Special clock, one of the two possible inputs of
                mixer mux.
+	c) hdmi: Gate of HDMI IP bus clock, needed together with sclk_hdmi.
 
 Example:
 

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -72,6 +72,7 @@ struct mixer_resources {
 	spinlock_t		reg_slock;
 	struct clk		*mixer;
 	struct clk		*vp;
+	struct clk		*hdmi;
 	struct clk		*sclk_mixer;
 	struct clk		*sclk_hdmi;
 	struct clk		*mout_mixer;
@@ -769,6 +770,12 @@ static int mixer_resources_init(struct mixer_context *mixer_ctx)
 		return -ENODEV;
 	}
 
+	mixer_res->hdmi = devm_clk_get(dev, "hdmi");
+	if (IS_ERR(mixer_res->hdmi)) {
+		dev_err(dev, "failed to get clock 'hdmi'\n");
+		return PTR_ERR(mixer_res->hdmi);
+	}
+
 	mixer_res->sclk_hdmi = devm_clk_get(dev, "sclk_hdmi");
 	if (IS_ERR(mixer_res->sclk_hdmi)) {
 		dev_err(dev, "failed to get clock 'sclk_hdmi'\n");
@@ -1092,6 +1099,7 @@ static void mixer_poweron(struct exynos_drm_crtc *crtc)
 	pm_runtime_get_sync(ctx->dev);
 
 	clk_prepare_enable(res->mixer);
+	clk_prepare_enable(res->hdmi);
 	if (ctx->vp_enabled) {
 		clk_prepare_enable(res->vp);
 		if (ctx->has_sclk)
@@ -1131,6 +1139,7 @@ static void mixer_poweroff(struct exynos_drm_crtc *crtc)
 	ctx->powered = false;
 	mutex_unlock(&ctx->mixer_mutex);
 
+	clk_disable_unprepare(res->hdmi);
 	clk_disable_unprepare(res->mixer);
 	if (ctx->vp_enabled) {
 		clk_disable_unprepare(res->vp);