video: ssd1307fb: Speed up the communication with the controller

The code until now was sending only 1pixel-wide page segment at once,
and started a new transfer every time. It has proven very inefficient,
because for one byte to display on the screen, we had to actually send 3
bytes over I2C: the address, the type of data that was going to the
controller, and then the actual data.

This patches changes that by sending a whole page at once, avoiding most
of this expensive overhead.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

diff --git a/drivers/video/ssd1307fb.c b/drivers/video/ssd1307fb.c
index 9daf058..04a4358 100644 (file)
--- a/drivers/video/ssd1307fb.c
+++ b/drivers/video/ssd1307fb.c
@@ -168,23 +168,28 @@ static void ssd1307fb_update_display(struct ssd1307fb_par *par)
         */
 
        for (i = 0; i < (par->height / 8); i++) {
+               struct ssd1307fb_array *array;
                ssd1307fb_write_cmd(par->client,
                                    SSD1307FB_START_PAGE_ADDRESS + i + par->page_offset);
                ssd1307fb_write_cmd(par->client, 0x00);
                ssd1307fb_write_cmd(par->client, 0x10);
 
+               array = ssd1307fb_alloc_array(par->width, SSD1307FB_DATA);
+
                for (j = 0; j < par->width; j++) {
-                       u8 buf = 0;
+                       array->data[j] = 0;
                        for (k = 0; k < 8; k++) {
                                u32 page_length = par->width * i;
                                u32 index = page_length + (par->width * k + j) / 8;
                                u8 byte = *(vmem + index);
                                u8 bit = byte & (1 << (j % 8));
                                bit = bit >> (j % 8);
-                               buf |= bit << k;
+                               array->data[j] |= bit << k;
                        }
-                       ssd1307fb_write_data(par->client, buf);
                }
+
+               ssd1307fb_write_array(par->client, array, par->width);
+               kfree(array);
        }
 }