drivers: ssd16xx: Remove SCREEN_INFO_DOUBLE_BUFFER cap

The SSD16xx driver used to use the SCREEN_INFO_DOUBLE_BUFFER flag to
indicate to the LVGL integration that it needs writes to be performed
twice. This was required because partial writes require both the old
and new buffer to be written.

This behavior is really an implementation detail and only applies to
partial refresh. Do this buffer maintenance in the driver instead.

Signed-off-by: Andreas Sandberg <[email protected]>

Author: andysan

drivers/display/ssd16xx.c

@@ -361,7 +361,7 @@ static int ssd16xx_set_window(const struct device *dev,
 			      const struct display_buffer_descriptor *desc)
 {
 	const struct ssd16xx_config *config = dev->config;
-	struct ssd16xx_data *data = dev->data;
+	const struct ssd16xx_data *data = dev->data;
 	int err;
 	uint16_t x_start;
 	uint16_t x_end;
@@ -445,7 +445,11 @@ static int ssd16xx_write(const struct device *dev, const uint16_t x,
 			 const struct display_buffer_descriptor *desc,
 			 const void *buf)
 {
+	const struct ssd16xx_config *config = dev->config;
 	const struct ssd16xx_data *data = dev->data;
+	const bool have_partial_refresh =
+		config->profiles[SSD16XX_PROFILE_PARTIAL] != NULL;
+	const bool partial_refresh = !data->blanking_on && have_partial_refresh;
 	const size_t buf_len = MIN(desc->buf_size,
 				   desc->height * desc->width / 8);
 	int err;
@@ -455,15 +459,13 @@ static int ssd16xx_write(const struct device *dev, const uint16_t x,
 		return -EINVAL;
 	}
 
-	if (!data->blanking_on) {
+	if (partial_refresh) {
 		/*
-		 * Blanking isn't on, so this is a partial
-		 * refresh. Request the partial profile. This
-		 * operation becomes a no-op if the profile is already
-		 * active.
+		 * Request the partial profile. This operation becomes
+		 * a no-op if the profile is already active.
 		 */
 		err = ssd16xx_set_profile(dev, SSD16XX_PROFILE_PARTIAL);
-		if (err < 0 && err != -ENOENT) {
+		if (err < 0) {
 			return -EIO;
 		}
 	}
@@ -486,6 +488,35 @@ static int ssd16xx_write(const struct device *dev, const uint16_t x,
 		}
 	}
 
+	if (data->blanking_on && have_partial_refresh) {
+		/*
+		 * We will trigger a full refresh when blanking is
+		 * turned off. The controller won't keep track of the
+		 * old frame buffer, which is needed to perform a
+		 * partial update, when this happens. Maintain the old
+		 * frame buffer manually here to make sure future
+		 * partial updates will work as expected.
+		 */
+		err = ssd16xx_write_cmd(dev, SSD16XX_CMD_WRITE_RED_RAM,
+					(uint8_t *)buf, buf_len);
+		if (err < 0) {
+			return err;
+		}
+	} else if (partial_refresh) {
+		/*
+		 * We just performed a partial refresh. After the
+		 * refresh, the controller swaps the black/red buffers
+		 * containing the current and new image. We need to
+		 * perform a second write here to ensure that future
+		 * updates work on an up-to-date framebuffer.
+		 */
+		err = ssd16xx_write_cmd(dev, SSD16XX_CMD_WRITE_RAM,
+					(uint8_t *)buf, buf_len);
+		if (err < 0) {
+			return err;
+		}
+	}
+
 	return 0;
 }
 
@@ -582,8 +613,7 @@ static void ssd16xx_get_capabilities(const struct device *dev,
 	caps->current_pixel_format = PIXEL_FORMAT_MONO10;
 	caps->screen_info = SCREEN_INFO_MONO_VTILED |
 			    SCREEN_INFO_MONO_MSB_FIRST |
-			    SCREEN_INFO_EPD |
-			    SCREEN_INFO_DOUBLE_BUFFER;
+			    SCREEN_INFO_EPD;
 }
 
 static int ssd16xx_set_orientation(const struct device *dev,