[4.2.y-ckt stable] Patch "i2c: img-scb: fix LOW and HIGH period values for the SCL clock" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    i2c: img-scb: fix LOW and HIGH period values for the SCL clock

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 786a3bb0e7ef58f4cd03a1c5e4bf8f2f74680703 Mon Sep 17 00:00:00 2001
From: Sifan Naeem <sifan.naeem at imgtec.com>
Date: Thu, 10 Sep 2015 15:50:04 +0100
Subject: i2c: img-scb: fix LOW and HIGH period values for the SCL clock

commit 987008dbc48479af250cddda7f36e920a47ef54f upstream.

Currently, after determining the minimum value for the High period
(TCKH) the remainder of the internal clock pulses is set as the Low
period (TCKL). This causes the i2c clock duty cycle to be much less
than 50%.

Modify the starting position to TCKH and TCKL at 50% of the internal
clock, and adjusts the TCKH and TCKL values from there should the
minimum value for TCKL not be met. This results in duty cycles closer
to 50%.

Fixes: commit 27bce457d588 ("i2c: img-scb: Add Imagination Technologies I2C SCB driver")
Signed-off-by: Sifan Naeem <sifan.naeem at imgtec.com>
Acked-by: James Hogan <james.hogan at imgtec.com>
Reviewed-by: James Hartley <james.hartley at imgtec.com>
Signed-off-by: Wolfram Sang <wsa at the-dreams.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/i2c/busses/i2c-img-scb.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/i2c/busses/i2c-img-scb.c b/drivers/i2c/busses/i2c-img-scb.c
index b4f59e1..e4daebc 100644
--- a/drivers/i2c/busses/i2c-img-scb.c
+++ b/drivers/i2c/busses/i2c-img-scb.c
@@ -1178,25 +1178,29 @@ static int img_i2c_init(struct img_i2c *i2c)
 	    ((bitrate_khz * clk_period) / 2))
 		int_bitrate++;

-	/* Setup TCKH value */
-	tckh = DIV_ROUND_UP(timing.tckh, clk_period);
+	/*
+	 * Setup clock duty cycle, start with 50% and adjust TCKH and TCKL
+	 * values from there if they don't meet minimum timing requirements
+	 */
+	tckh = int_bitrate / 2;
+	tckl = int_bitrate - tckh;

-	if (tckh > 0)
-		data = tckh - 1;
-	else
-		data = 0;
+	/* Adjust TCKH and TCKL values */
+	data = DIV_ROUND_UP(timing.tckl, clk_period);

-	img_i2c_writel(i2c, SCB_TIME_TCKH_REG, data);
+	if (tckl < data) {
+		tckl = data;
+		tckh = int_bitrate - tckl;
+	}

-	/* Setup TCKL value */
-	tckl = int_bitrate - tckh;
+	if (tckh > 0)
+		--tckh;

 	if (tckl > 0)
-		data = tckl - 1;
-	else
-		data = 0;
+		--tckl;

-	img_i2c_writel(i2c, SCB_TIME_TCKL_REG, data);
+	img_i2c_writel(i2c, SCB_TIME_TCKH_REG, tckh);
+	img_i2c_writel(i2c, SCB_TIME_TCKL_REG, tckl);

 	/* Setup TSDH value */
 	tsdh = DIV_ROUND_UP(timing.tsdh, clk_period);
--
1.9.1