[PATCH 1/4] ARM: cfa10036: dt: Change i2c0 clock frequency

[PATCH 1/4] ARM: cfa10036: dt: Change i2c0 clock frequency

[Maxime Ripard]

The OLED display can work faster. Change the i2c controller clock
frequency to remove the tearing effect that can be seen on the display.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 arch/arm/boot/dts/imx28-cfa10036.dts |    1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/boot/dts/imx28-cfa10036.dts b/arch/arm/boot/dts/imx28-cfa10036.dts
index 40488f5a8..a524caf 100644
--- a/arch/arm/boot/dts/imx28-cfa10036.dts
+++ b/arch/arm/boot/dts/imx28-cfa10036.dts
@@ -67,6 +67,7 @@
 			i2c0: i2c@80058000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&i2c0_pins_b>;
+				clock-frequency = <400000>;
 				status = "okay";
 
 				ssd1306: oled@3c {
-- 
1.7.10.4

Re: [PATCH 1/4] ARM: cfa10036: dt: Change i2c0 clock frequency

[Shawn Guo]

On Mon, Apr 22, 2013 at 12:02:22PM +0200, Maxime Ripard wrote:
> The OLED display can work faster. Change the i2c controller clock
> frequency to remove the tearing effect that can be seen on the display.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Applied, thanks.

[PATCH 2/4] ssd1307fb: Rework the communication functions

[Maxime Ripard]

To efficiently send a whole page to the display, we need to be able to
manipulate more easily the data arrays that has to be sent to the OLED
controller. As such, this patch introduces a ssd1307fb_array structure
that handles both the small header to be sent over i2c, which contains
the type of information sent, and the raw bytes after that.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/video/ssd1307fb.c |   77 +++++++++++++++++++++++++++++----------------
 1 file changed, 50 insertions(+), 27 deletions(-)

diff --git a/drivers/video/ssd1307fb.c b/drivers/video/ssd1307fb.c
index 5ab5281..35f5348 100644
--- a/drivers/video/ssd1307fb.c
+++ b/drivers/video/ssd1307fb.c
@@ -51,6 +51,11 @@ struct ssd1307fb_par {
 	u32 width;
 };
 
+struct ssd1307fb_array {
+	u8	type;
+	u8	data[0];
+};
+
 static struct fb_fix_screeninfo ssd1307fb_fix = {
 	.id		= "Solomon SSD1307",
 	.type		= FB_TYPE_PACKED_PIXELS,
@@ -65,49 +70,67 @@ static struct fb_var_screeninfo ssd1307fb_var = {
 	.bits_per_pixel	= 1,
 };
 
-static int ssd1307fb_write_array(struct i2c_client *client, u8 type, u8 *cmd, u32 len)
+static struct ssd1307fb_array *ssd1307fb_alloc_array(u32 len, u8 type)
 {
-	u8 *buf;
-	int ret = 0;
-
-	buf = kzalloc(len + 1, GFP_KERNEL);
-	if (!buf) {
-		dev_err(&client->dev, "Couldn't allocate sending buffer.\n");
-		return -ENOMEM;
-	}
+	struct ssd1307fb_array *array;
 
-	buf[0] = type;
-	memcpy(buf + 1, cmd, len);
+	array = kzalloc(sizeof(struct ssd1307fb_array) + len, GFP_KERNEL);
+	if (!array)
+		return NULL;
 
-	ret = i2c_master_send(client, buf, len + 1);
-	if (ret != len + 1) {
-		dev_err(&client->dev, "Couldn't send I2C command.\n");
-		goto error;
-	}
+	array->type = type;
 
-error:
-	kfree(buf);
-	return ret;
+	return array;
 }
 
-static inline int ssd1307fb_write_cmd_array(struct i2c_client *client, u8 *cmd, u32 len)
+static int ssd1307fb_write_array(struct i2c_client *client,
+				 struct ssd1307fb_array *array, u32 len)
 {
-	return ssd1307fb_write_array(client, SSD1307FB_COMMAND, cmd, len);
+	int ret;
+
+	len += sizeof(struct ssd1307fb_array);
+
+	ret = i2c_master_send(client, (u8 *)array, len);
+	if (ret != len) {
+		dev_err(&client->dev, "Couldn't send I2C command.\n");
+		return ret;
+	}
+
+	return 0;
 }
 
 static inline int ssd1307fb_write_cmd(struct i2c_client *client, u8 cmd)
 {
-	return ssd1307fb_write_cmd_array(client, &cmd, 1);
-}
+	struct ssd1307fb_array *array;
+	int ret;
 
-static inline int ssd1307fb_write_data_array(struct i2c_client *client, u8 *cmd, u32 len)
-{
-	return ssd1307fb_write_array(client, SSD1307FB_DATA, cmd, len);
+	array = ssd1307fb_alloc_array(1, SSD1307FB_COMMAND);
+	if (!array)
+		return -ENOMEM;
+
+	array->data[0] = cmd;
+
+	ret = ssd1307fb_write_array(client, array, 1);
+	kfree(array);
+
+	return ret;
 }
 
 static inline int ssd1307fb_write_data(struct i2c_client *client, u8 data)
 {
-	return ssd1307fb_write_data_array(client, &data, 1);
+	struct ssd1307fb_array *array;
+	int ret;
+
+	array = ssd1307fb_alloc_array(1, SSD1307FB_DATA);
+	if (!array)
+		return -ENOMEM;
+
+	array->data[0] = data;
+
+	ret = ssd1307fb_write_array(client, array, 1);
+	kfree(array);
+
+	return ret;
 }
 
 static void ssd1307fb_update_display(struct ssd1307fb_par *par)
-- 
1.7.10.4

[PATCH 3/4] ssd1307fb: Speed up the communication with the controller

[Maxime Ripard]

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>
---
 drivers/video/ssd1307fb.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/video/ssd1307fb.c b/drivers/video/ssd1307fb.c
index 35f5348..cab5f7c 100644
--- 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);
 	}
 }
 
-- 
1.7.10.4

[PATCH 4/4] ssd1307fb: Make use of horizontal addressing mode

[Maxime Ripard]

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>
---
 drivers/video/ssd1307fb.c |   51 +++++++++++++++++++++++++++++++++------------
 1 file changed, 38 insertions(+), 13 deletions(-)

diff --git a/drivers/video/ssd1307fb.c b/drivers/video/ssd1307fb.c
index cab5f7c..259c9ee 100644
--- 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)
-- 
1.7.10.4