Re: [PATCH v3 3/6] i2c: at91: Send bus clear command if SDA is down

On Wed, Jan 15, 2020 at 01:54:19PM +0200, Codrin Ciubotariu wrote:

After a transfer timeout, some faulty I2C slave devices might hold down
the SDA pin. We can generate a bus clear command, hoping that the slave
might release the pins.
If the CLEAR command is not supported, we will use gpio recovery, if
available, to reset the bus.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>

One thing to improve:

+	/*
+	 * some faulty I2C slave devices might hold SDA down;
+	 * we can send a bus clear command, hoping that the pins will be
+	 * released
+	 */
+	if (has_clear_cmd) {
+		if (!(dev->transfer_status & AT91_TWI_SDA)) {
+			dev_dbg(dev->dev,
+				"SDA is down; sending bus clear command\n");
+			if (dev->use_alt_cmd) {
+				unsigned int acr;
+
+				acr = at91_twi_read(dev, AT91_TWI_ACR);
+				acr &= ~AT91_TWI_ACR_DATAL_MASK;
+				at91_twi_write(dev, AT91_TWI_ACR, acr);
+			}
+			at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_CLEAR);
+		}

The inner if-block should be a seperate function, then you could do in
probe:

	if (has_clear_cmd)
		rinfo->recover_bus = <the above function>;
	else
		rinfo->recover_bus = i2c_generic_scl_recovery;

Then, i2c_recover_bus() will always do the right thing. More readable
and better maintainable IMO.

If this is not possible (maybe I overlooked some logic), then maybe this
will work:

	rinfo->recover_bus = <your custom function>;

and put the

	if (has_clear_cmd)

block there.