drm/mipi-dbi: Support separate I/O regulator

The MIPI DBI specification defines separate vdd (panel power) and
vddi (I/O voltage) supplies. Displays that require different voltages
for the different supplies do exist, so the supplies cannot be
combined into one as they are now. Add a new io_regulator property to
the mipi_dbi_dev struct which can be set by the panel driver along
with the regulator property.

Signed-off-by: Otto Pflüger <[e-mail]>
Reviewed-by: Noralf Trønnes <[e-mail]>
Signed-off-by: Noralf Trønnes <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_mipi_dbi.c

···
 
 	if (dbidev->regulator)
 		regulator_disable(dbidev->regulator);
+	if (dbidev->io_regulator)
+		regulator_disable(dbidev->io_regulator);
 }
 EXPORT_SYMBOL(mipi_dbi_pipe_disable);
 
···
 		}
 	}
 
+	if (dbidev->io_regulator) {
+		ret = regulator_enable(dbidev->io_regulator);
+		if (ret) {
+			DRM_DEV_ERROR(dev, "Failed to enable I/O regulator (%d)\n", ret);
+			if (dbidev->regulator)
+				regulator_disable(dbidev->regulator);
+			return ret;
+		}
+	}
+
 	if (cond && mipi_dbi_display_is_on(dbi))
 		return 1;
 
···
 		DRM_DEV_ERROR(dev, "Failed to send reset command (%d)\n", ret);
 		if (dbidev->regulator)
 			regulator_disable(dbidev->regulator);
+		if (dbidev->io_regulator)
+			regulator_disable(dbidev->io_regulator);
 		return ret;
 	}
 

include/drm/drm_mipi_dbi.h

···
 	struct backlight_device *backlight;
 
 	/**
-	 * @regulator: power regulator (optional)
+	 * @regulator: power regulator (Vdd) (optional)
 	 */
 	struct regulator *regulator;
+
+	/**
+	 * @io_regulator: I/O power regulator (Vddi) (optional)
+	 */
+	struct regulator *io_regulator;
 
 	/**
 	 * @dbi: MIPI DBI interface