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

Wolfram Sang
2020-02-22T11:44:39Z

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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.

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