From cf8ce8b80f8bf9669f6ec4e71e16668430febdac Mon Sep 17 00:00:00 2001
From: Russell King <rmk+kernel@armlinux.org.uk>
Date: Sun, 15 Dec 2019 16:39:05 +0000
Subject: [PATCH] i2c: fix bus recovery stop mode timing
Git-commit: cf8ce8b80f8bf9669f6ec4e71e16668430febdac
Patch-mainline: v5.5-rc6
References: git-fixes

The I2C specification states that tsu:sto for standard mode timing must
be at minimum 4us. Pictographically, this is:

Scl: ____/~~~~~~~~~
Sda: _________/~~~~       ->|    |<- 4us minimum

We are currently waiting 2.5us between asserting SCL and SDA, which is
in violation of the standard. Adjust the timings to ensure that we meet
what is stipulated as the minimum timings to ensure that all devices
correctly interpret the STOP bus transition.

This is more important than trying to generate a square wave with even
duty cycle.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/i2c/i2c-core-base.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 9f8dcd3f8385..35b209797d7b 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -186,10 +186,11 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 	 * If we can set SDA, we will always create a STOP to ensure additional
 	 * pulses will do no harm. This is achieved by letting SDA follow SCL
 	 * half a cycle later. Check the 'incomplete_write_byte' fault injector
-	 * for details.
+	 * for details. Note that we must honour tsu:sto, 4us, but lets use 5us
+	 * here for simplicity.
 	 */
 	bri->set_scl(adap, scl);
-	ndelay(RECOVERY_NDELAY / 2);
+	ndelay(RECOVERY_NDELAY);
 	if (bri->set_sda)
 		bri->set_sda(adap, scl);
 	ndelay(RECOVERY_NDELAY / 2);
@@ -211,7 +212,13 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 		scl = !scl;
 		bri->set_scl(adap, scl);
 		/* Creating STOP again, see above */
-		ndelay(RECOVERY_NDELAY / 2);
+		if (scl)  {
+			/* Honour minimum tsu:sto */
+			ndelay(RECOVERY_NDELAY);
+		} else {
+			/* Honour minimum tf and thd:dat */
+			ndelay(RECOVERY_NDELAY / 2);
+		}
 		if (bri->set_sda)
 			bri->set_sda(adap, scl);
 		ndelay(RECOVERY_NDELAY / 2);
-- 
2.16.4