drm/dsi: Implement set tear scanline

Provide a small convenience wrapper that transmits
a set_tear_scanline command.

v2:
  * helper function suggested by Thierry
    for set_tear_scanline
  * Also includes small build fixes from Sumit Semwal.

v3: one scanline parameter suggested by jani

v4: passing the payload properly as suggested by jani

Cc: Archit Taneja <archit.taneja@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Vinay Simha BN <simhavcs@gmail.com>
Reviewed-by: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465285532-12676-1-git-send-email-simhavcs@gmail.com

drivers/gpu/drm/drm_mipi_dsi.c

@@ -982,6 +982,28 @@ int mipi_dsi_dcs_set_tear_on(struct mipi_dsi_device *dsi,
 }
 EXPORT_SYMBOL(mipi_dsi_dcs_set_tear_on);
 
+/**
+ * mipi_dsi_set_tear_scanline() - turn on the display module's Tearing Effect
+ * output signal on the TE signal line when display module reaches line N
+ * defined by STS[n:0].
+ * @dsi: DSI peripheral device
+ * @param: STS[10:0]
+ * Return: 0 on success or a negative error code on failure
+ */
+int mipi_dsi_set_tear_scanline(struct mipi_dsi_device *dsi, u16 param)
+{
+	u8 payload[3] = { MIPI_DCS_SET_TEAR_SCANLINE, param >> 8,
+			  param & 0xff };
+	ssize_t err;
+
+	err = mipi_dsi_generic_write(dsi, payload, sizeof(payload));
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+EXPORT_SYMBOL(mipi_dsi_set_tear_scanline);
+
 /**
  * mipi_dsi_dcs_set_pixel_format() - sets the pixel format for the RGB image
  *    data used by the interface

include/drm/drm_mipi_dsi.h

@@ -263,6 +263,7 @@ int mipi_dsi_dcs_set_column_address(struct mipi_dsi_device *dsi, u16 start,
 				    u16 end);
 int mipi_dsi_dcs_set_page_address(struct mipi_dsi_device *dsi, u16 start,
 				  u16 end);
+int mipi_dsi_set_tear_scanline(struct mipi_dsi_device *dsi, u16 param);
 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);