video: ssd1307fb: Make use of horizontal addressing mode

By default, the ssd1307 controller uses an addressing mode called page
addressing. This mode only increments the column cursor in memory when
writing data but will not increments the page cursor when we are at the
end of the page.

However, the controller supports another addressing mode, called
horizontal addressing, that will maintain both the page and column
cursors when writing data to the controller.

That means that we can just remove the code that increments the current
page address and reset the column cursor when reaching the end of the
line, allowing to have a lower data overhead, and a simpler driver.

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 04a435886855163dfc371b8d2698e5e3a7b7b349..44967c8fef2b5a344d9e6a78e1339e148f2fbd20 100644 (file)
--- a/drivers/video/ssd1307fb.c
+++ b/drivers/video/ssd1307fb.c
@@ -19,6 +19,12 @@
 #define SSD1307FB_DATA                 0x40
 #define SSD1307FB_COMMAND              0x80
 
+#define SSD1307FB_SET_ADDRESS_MODE     0x20
+#define SSD1307FB_SET_ADDRESS_MODE_HORIZONTAL  (0x00)
+#define SSD1307FB_SET_ADDRESS_MODE_VERTICAL    (0x01)
+#define SSD1307FB_SET_ADDRESS_MODE_PAGE                (0x02)
+#define SSD1307FB_SET_COL_RANGE                0x21
+#define SSD1307FB_SET_PAGE_RANGE       0x22
 #define SSD1307FB_CONTRAST             0x81
 #define        SSD1307FB_CHARGE_PUMP           0x8d
 #define SSD1307FB_SEG_REMAP_ON         0xa1
@@ -135,9 +141,15 @@ static inline int ssd1307fb_write_data(struct i2c_client *client, u8 data)
 
 static void ssd1307fb_update_display(struct ssd1307fb_par *par)
 {
+       struct ssd1307fb_array *array;
        u8 *vmem = par->info->screen_base;
        int i, j, k;
 
+       array = ssd1307fb_alloc_array(par->width * par->height / 8,
+                                     SSD1307FB_DATA);
+       if (!array)
+               return;
+
        /*
         * The screen is divided in pages, each having a height of 8
         * pixels, and the width of the screen. When sending a byte of
@@ -168,29 +180,22 @@ 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++) {
-                       array->data[j] = 0;
+                       u32 array_idx = i * par->width + j;
+                       array->data[array_idx] = 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);
-                               array->data[j] |= bit << k;
+                               array->data[array_idx] |= bit << k;
                        }
                }
-
-               ssd1307fb_write_array(par->client, array, par->width);
-               kfree(array);
        }
+
+       ssd1307fb_write_array(par->client, array, par->width * par->height / 8);
+       kfree(array);
 }
 
 
@@ -371,6 +376,26 @@ static int ssd1307fb_ssd1306_init(struct ssd1307fb_par *par)
        if (ret < 0)
                return ret;
 
+       /* Switch to horizontal addressing mode */
+       ret = ssd1307fb_write_cmd(par->client, SSD1307FB_SET_ADDRESS_MODE);
+       ret = ret & ssd1307fb_write_cmd(par->client,
+                                       SSD1307FB_SET_ADDRESS_MODE_HORIZONTAL);
+       if (ret < 0)
+               return ret;
+
+       ret = ssd1307fb_write_cmd(par->client, SSD1307FB_SET_COL_RANGE);
+       ret = ret & ssd1307fb_write_cmd(par->client, 0x0);
+       ret = ret & ssd1307fb_write_cmd(par->client, par->width - 1);
+       if (ret < 0)
+               return ret;
+
+       ret = ssd1307fb_write_cmd(par->client, SSD1307FB_SET_PAGE_RANGE);
+       ret = ret & ssd1307fb_write_cmd(par->client, 0x0);
+       ret = ret & ssd1307fb_write_cmd(par->client,
+                                       par->page_offset + (par->height / 8) - 1);
+       if (ret < 0)
+               return ret;
+
        /* Turn on the display */
        ret = ssd1307fb_write_cmd(par->client, SSD1307FB_DISPLAY_ON);
        if (ret < 0)