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Commit 3394e645 authored by Maxime Ripard's avatar Maxime Ripard Committed by Tomi Valkeinen
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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: default avatarMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: default avatarTomi Valkeinen <tomi.valkeinen@ti.com>
parent 9f7714d4

drivers/video/ssd1307fb.c

+8 −3
Original line number Diff line number Diff line
@@ -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);

	}

}