drm/panel: sitronix-st7789v: add support for partial mode

The ST7789V controller features support for the partial mode. Here,
the area to be displayed can be restricted in one direction (by default,
in vertical direction). This is useful for panels that are partially
occluded by design. Add support for the partial mode.

Signed-off-by: Michael Riesch <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Signed-off-by: Neil Armstrong <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/panel/panel-sitronix-st7789v.c

···
 	u32 bus_format;
 	u32 bus_flags;
 	bool invert_mode;
+	bool partial_mode;
+	u16 partial_start;
+	u16 partial_end;
 };
 
 struct st7789v {
···
 static int st7789v_prepare(struct drm_panel *panel)
 {
 	struct st7789v *ctx = panel_to_st7789v(panel);
-	u8 pixel_fmt, polarity;
+	u8 mode, pixel_fmt, polarity;
 	int ret;
+
+	if (!ctx->info->partial_mode)
+		mode = ST7789V_RGBCTRL_WO;
+	else
+		mode = 0;
 
 	switch (ctx->info->bus_format) {
 	case MEDIA_BUS_FMT_RGB666_1X18:
···
 						MIPI_DCS_EXIT_INVERT_MODE));
 	}
 
+	if (ctx->info->partial_mode) {
+		u8 area_data[4] = {
+			(ctx->info->partial_start >> 8) & 0xff,
+			(ctx->info->partial_start >> 0) & 0xff,
+			((ctx->info->partial_end - 1) >> 8) & 0xff,
+			((ctx->info->partial_end - 1) >> 0) & 0xff,
+		};
+
+		/* Caution: if userspace ever pushes a mode different from the
+		 * expected one (i.e., the one advertised by get_modes), we'll
+		 * add margins.
+		 */
+
+		ST7789V_TEST(ret, st7789v_write_command(
+					  ctx, MIPI_DCS_ENTER_PARTIAL_MODE));
+
+		ST7789V_TEST(ret, st7789v_write_command(
+					  ctx, MIPI_DCS_SET_PAGE_ADDRESS));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[0]));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[1]));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[2]));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[3]));
+
+		ST7789V_TEST(ret, st7789v_write_command(
+					  ctx, MIPI_DCS_SET_PARTIAL_ROWS));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[0]));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[1]));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[2]));
+		ST7789V_TEST(ret, st7789v_write_data(ctx, area_data[3]));
+	}
+
 	ST7789V_TEST(ret, st7789v_write_command(ctx, ST7789V_RAMCTRL_CMD));
 	ST7789V_TEST(ret, st7789v_write_data(ctx, ST7789V_RAMCTRL_DM_RGB |
 					     ST7789V_RAMCTRL_RM_RGB));
···
 					     ST7789V_RAMCTRL_MAGIC));
 
 	ST7789V_TEST(ret, st7789v_write_command(ctx, ST7789V_RGBCTRL_CMD));
-	ST7789V_TEST(ret, st7789v_write_data(ctx, ST7789V_RGBCTRL_WO |
+	ST7789V_TEST(ret, st7789v_write_data(ctx, mode |
 					     ST7789V_RGBCTRL_RCM(2) |
 					     polarity));
 	ST7789V_TEST(ret, st7789v_write_data(ctx, ST7789V_RGBCTRL_VBP(8)));