drm/tegra: dsi - Implement VDD supply support

The DSI controllers are powered by a (typically 1.2V) regulator. Usually
this is always on, so there was no need to support enabling or disabling
it thus far. But in order not to consume any power when DSI is inactive,
give the driver a chance to enable or disable the supply as needed.

Signed-off-by: Thierry Reding <[e-mail]>

Documentation/devicetree/bindings/gpu/nvidia,tegra20-host1x.txt

···
     See ../reset/reset.txt for details.
   - reset-names: Must include the following entries:
     - dsi
+  - avdd-dsi-supply: phandle of a supply that powers the DSI controller
   - nvidia,mipi-calibrate: Should contain a phandle and a specifier specifying
     which pads are used by this DSI output and need to be calibrated. See also
     ../mipi/nvidia,tegra114-mipi.txt.

drivers/gpu/drm/tegra/dsi.c

···
 #include <linux/platform_device.h>
 #include <linux/reset.h>
 
+#include <linux/regulator/consumer.h>
+
 #include <drm/drm_mipi_dsi.h>
 #include <drm/drm_panel.h>
 
···
 
 	struct tegra_mipi_device *mipi;
 	struct mipi_dsi_host host;
+
+	struct regulator *vdd;
 };
 
 static inline struct tegra_dsi *
···
 		return err;
 	}
 
+	dsi->vdd = devm_regulator_get(&pdev->dev, "avdd-dsi-csi");
+	if (IS_ERR(dsi->vdd)) {
+		dev_err(&pdev->dev, "cannot get VDD supply\n");
+		return PTR_ERR(dsi->vdd);
+	}
+
+	err = regulator_enable(dsi->vdd);
+	if (err < 0) {
+		dev_err(&pdev->dev, "cannot enable VDD supply\n");
+		return err;
+	}
+
 	err = tegra_dsi_setup_clocks(dsi);
 	if (err < 0) {
 		dev_err(&pdev->dev, "cannot setup clocks\n");
···
 	mipi_dsi_host_unregister(&dsi->host);
 	tegra_mipi_free(dsi->mipi);
 
+	regulator_disable(dsi->vdd);
 	clk_disable_unprepare(dsi->clk_parent);
 	clk_disable_unprepare(dsi->clk_lp);
 	clk_disable_unprepare(dsi->clk);