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i2c: fix bus recovery stop mode timing

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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>
This commit is contained in:
Russell King 2019-12-15 16:39:05 +00:00 committed by Wolfram Sang
parent 3b722da667
commit cf8ce8b80f
1 changed files with 10 additions and 3 deletions
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13
drivers/i2c/i2c-core-base.c
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@ -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);