[PATCH 5/5] video: fbdev: ssd1307fb: Cache address ranges

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Cache the column and page ranges, to avoid doing unneeded I2C transfers
when the values haven't changed.

Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
---
 drivers/video/fbdev/ssd1307fb.c | 52 +++++++++++++++++++++++----------
 1 file changed, 36 insertions(+), 16 deletions(-)

diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c
index 8e3d4be74723b9bf..23b43ce479898813 100644
--- a/drivers/video/fbdev/ssd1307fb.c
+++ b/drivers/video/fbdev/ssd1307fb.c
@@ -82,6 +82,11 @@ struct ssd1307fb_par {
 	struct regulator *vbat_reg;
 	u32 vcomh;
 	u32 width;
+	/* Cached address ranges */
+	u8 col_start;
+	u8 col_end;
+	u8 page_start;
+	u8 page_end;
 };
 
 struct ssd1307fb_array {
@@ -160,28 +165,43 @@ static int ssd1307fb_set_address_range(struct ssd1307fb_par *par, u8 col_start,
 	int ret;
 
 	/* Set column range */
-	ret = ssd1307fb_write_cmd(par->client, SSD1307FB_SET_COL_RANGE);
-	if (ret < 0)
-		return ret;
+	if (col_start != par->col_start || col_end != par->col_end) {
+		ret = ssd1307fb_write_cmd(par->client, SSD1307FB_SET_COL_RANGE);
+		if (ret < 0)
+			return ret;
 
-	ret = ssd1307fb_write_cmd(par->client, col_start);
-	if (ret < 0)
-		return ret;
+		ret = ssd1307fb_write_cmd(par->client, col_start);
+		if (ret < 0)
+			return ret;
 
-	ret = ssd1307fb_write_cmd(par->client, col_end);
-	if (ret < 0)
-		return ret;
+		ret = ssd1307fb_write_cmd(par->client, col_end);
+		if (ret < 0)
+			return ret;
+
+		par->col_start = col_start;
+		par->col_end = col_end;
+	}
 
 	/* Set page range */
-	ret = ssd1307fb_write_cmd(par->client, SSD1307FB_SET_PAGE_RANGE);
-	if (ret < 0)
-		return ret;
+	if (page_start != par->page_start || page_end != par->page_end) {
+		ret = ssd1307fb_write_cmd(par->client,
+					  SSD1307FB_SET_PAGE_RANGE);
+		if (ret < 0)
+			return ret;
 
-	ret = ssd1307fb_write_cmd(par->client, page_start);
-	if (ret < 0)
-		return ret;
+		ret = ssd1307fb_write_cmd(par->client, page_start);
+		if (ret < 0)
+			return ret;
+
+		ret = ssd1307fb_write_cmd(par->client, page_end);
+		if (ret < 0)
+			return ret;
 
-	return ssd1307fb_write_cmd(par->client, page_end);
+		par->page_start = page_start;
+		par->page_end = page_end;
+	}
+
+	return 0;
 }
 
 static int ssd1307fb_update_rect(struct ssd1307fb_par *par, unsigned int x,
-- 
2.25.1