drm/mediatek: mtk_dpi: Add support for DPI input clock from HDMI

On some SoCs, like MT8195 and MT8188, the DPI instance that is
reserved to the HDMI Transmitter uses a different clock topology.

In this case, the DPI is clocked by the HDMI IP, and this outputs
its clock to the MM input of dpi_pixel_clk, which is essential to
enable register access to the DPI IP.

Add a `clocked_by_hdmi` member to struct mtk_dpi_conf, and check
it to avoid enabling the DPI clocks in the mediatek-drm internal
.start() callback (and avoid disabing in the .stop() component
callback): this will make sure that the clock configuration
sequence is respected during display pipeline setup by following
the bridge ops between DPI and HDMI, where the HDMI driver is
expected to enable the clocks in the bridge's pre_enable(), and
DPI in the enable() cb.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

Author: AngeloGioacchino Del Regno

drivers/gpu/drm/mediatek/mtk_dpi.c

@@ -145,6 +145,8 @@ struct mtk_dpi_factor {
  *		     If present, implies that the feature must be enabled.
  * @pixels_per_iter: Quantity of transferred pixels per iteration.
  * @edge_cfg_in_mmsys: If the edge configuration for DPI's output needs to be set in MMSYS.
+ * @clocked_by_hdmi: HDMI IP outputs clock to dpi_pixel_clk input clock, needed
+ *		     for DPI registers access.
  */
 struct mtk_dpi_conf {
 	const struct mtk_dpi_factor *dpi_factor;
@@ -165,6 +167,7 @@ struct mtk_dpi_conf {
 	u32 input_2p_en_bit;
 	u32 pixels_per_iter;
 	bool edge_cfg_in_mmsys;
+	bool clocked_by_hdmi;
 };
 
 static void mtk_dpi_mask(struct mtk_dpi *dpi, u32 offset, u32 val, u32 mask)
@@ -585,7 +588,9 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
 	struct videomode vm = { 0 };
 
 	drm_display_mode_to_videomode(mode, &vm);
-	mtk_dpi_set_pixel_clk(dpi, &vm, mode->clock);
+
+	if (!dpi->conf->clocked_by_hdmi)
+		mtk_dpi_set_pixel_clk(dpi, &vm, mode->clock);
 
 	dpi_pol.ck_pol = MTK_DPI_POLARITY_FALLING;
 	dpi_pol.de_pol = MTK_DPI_POLARITY_RISING;
@@ -920,14 +925,16 @@ void mtk_dpi_start(struct device *dev)
 {
 	struct mtk_dpi *dpi = dev_get_drvdata(dev);
 
-	mtk_dpi_power_on(dpi);
+	if (!dpi->conf->clocked_by_hdmi)
+		mtk_dpi_power_on(dpi);
 }
 
 void mtk_dpi_stop(struct device *dev)
 {
 	struct mtk_dpi *dpi = dev_get_drvdata(dev);
 
-	mtk_dpi_power_off(dpi);
+	if (!dpi->conf->clocked_by_hdmi)
+		mtk_dpi_power_off(dpi);
 }
 
 unsigned int mtk_dpi_encoder_index(struct device *dev)