drm/mediatek: mtk_dpi: Explicitly manage TVD clock in power on/off

In preparation for adding support for MT8195's HDMI reserved
DPI, add calls to clk_prepare_enable() / clk_disable_unprepare()
for the TVD clock: in this particular case, the aforementioned
clock is not (and cannot be) parented to neither pixel or engine
clocks hence it won't get enabled automatically by the clock
framework.

Please note that on all of the currently supported MediaTek
platforms, the TVD clock is always a parent of either pixel or
engine clocks, and this means that the common clock framework
is already enabling this clock before the children.
On such platforms, this commit will only increase the refcount
of the TVD clock without any functional change.

Reviewed-by: CK Hu <[email protected]>
Signed-off-by: AngeloGioacchino Del Regno <[email protected]>
Link: https://patchwork.kernel.org/project/dri-devel/patch/[email protected]/
Signed-off-by: Chun-Kuang Hu <[email protected]>

Author: AngeloGioacchino Del Regno

drivers/gpu/drm/mediatek/mtk_dpi.c

@@ -499,6 +499,7 @@ static void mtk_dpi_power_off(struct mtk_dpi *dpi)
 
 	mtk_dpi_disable(dpi);
 	clk_disable_unprepare(dpi->pixel_clk);
+	clk_disable_unprepare(dpi->tvd_clk);
 	clk_disable_unprepare(dpi->engine_clk);
 }
 
@@ -515,6 +516,12 @@ static int mtk_dpi_power_on(struct mtk_dpi *dpi)
 		goto err_refcount;
 	}
 
+	ret = clk_prepare_enable(dpi->tvd_clk);
+	if (ret) {
+		dev_err(dpi->dev, "Failed to enable tvd pll: %d\n", ret);
+		goto err_engine;
+	}
+
 	ret = clk_prepare_enable(dpi->pixel_clk);
 	if (ret) {
 		dev_err(dpi->dev, "Failed to enable pixel clock: %d\n", ret);
@@ -524,6 +531,8 @@ static int mtk_dpi_power_on(struct mtk_dpi *dpi)
 	return 0;
 
 err_pixel:
+	clk_disable_unprepare(dpi->tvd_clk);
+err_engine:
 	clk_disable_unprepare(dpi->engine_clk);
 err_refcount:
 	dpi->refcount--;