drm/dsi: Implement DCS {get,set}_pixel_format commands

Provide small convenience wrappers to query or set the pixel format used
by the interface.

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

drivers/gpu/drm/drm_mipi_dsi.c

···
 EXPORT_SYMBOL(mipi_dsi_dcs_get_power_mode);
 
 /**
+ * mipi_dsi_dcs_get_pixel_format() - gets the pixel format for the RGB image
+ *    data used by the interface
+ * @dsi: DSI peripheral device
+ * @format: return location for the pixel format
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int mipi_dsi_dcs_get_pixel_format(struct mipi_dsi_device *dsi, u8 *format)
+{
+	ssize_t err;
+
+	err = mipi_dsi_dcs_read(dsi, MIPI_DCS_GET_PIXEL_FORMAT, format,
+				sizeof(*format));
+	if (err <= 0) {
+		if (err == 0)
+			err = -ENODATA;
+
+		return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(mipi_dsi_dcs_get_pixel_format);
+
+/**
  * mipi_dsi_dcs_enter_sleep_mode() - disable all unnecessary blocks inside the
  *    display module except interface communication
  * @dsi: DSI peripheral device
···
 	return 0;
 }
 EXPORT_SYMBOL(mipi_dsi_dcs_set_tear_on);
+
+/**
+ * mipi_dsi_dcs_set_pixel_format() - sets the pixel format for the RGB image
+ *    data used by the interface
+ * @dsi: DSI peripheral device
+ * @format: pixel format
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int mipi_dsi_dcs_set_pixel_format(struct mipi_dsi_device *dsi, u8 format)
+{
+	ssize_t err;
+
+	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_PIXEL_FORMAT, &format,
+				 sizeof(format));
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+EXPORT_SYMBOL(mipi_dsi_dcs_set_pixel_format);
 
 static int mipi_dsi_drv_probe(struct device *dev)
 {

include/drm/drm_mipi_dsi.h

···
 int mipi_dsi_dcs_nop(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_soft_reset(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_get_power_mode(struct mipi_dsi_device *dsi, u8 *mode);
+int mipi_dsi_dcs_get_pixel_format(struct mipi_dsi_device *dsi, u8 *format);
 int mipi_dsi_dcs_enter_sleep_mode(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_exit_sleep_mode(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_set_display_off(struct mipi_dsi_device *dsi);
···
 int mipi_dsi_dcs_set_tear_off(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_set_tear_on(struct mipi_dsi_device *dsi,
 			     enum mipi_dsi_dcs_tear_mode mode);
+int mipi_dsi_dcs_set_pixel_format(struct mipi_dsi_device *dsi, u8 format);
 
 /**
  * struct mipi_dsi_driver - DSI driver