On 19.09.2019 18:06, kbouhara wrote:
>
> On 9/11/19 11:58 AM, Codrin Ciubotariu wrote:
>> After a transfer timeout, some faulty I2C slave devices might hold down
>> the SCL or the SDA pins. We can generate a bus clear command, hoping that
>> the slave might release the pins.
>>
>> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@xxxxxxxxxxxxx>
>> ---
>> drivers/i2c/busses/i2c-at91-master.c | 20 ++++++++++++++++++++
>> drivers/i2c/busses/i2c-at91.h | 6 +++++-
>> 2 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-at91-master.c
>> b/drivers/i2c/busses/i2c-at91-master.c
>> index a3fcc35ffd3b..5f544a16db96 100644
>> --- a/drivers/i2c/busses/i2c-at91-master.c
>> +++ b/drivers/i2c/busses/i2c-at91-master.c
>> @@ -599,6 +599,26 @@ static int at91_do_twi_transfer(struct
>> at91_twi_dev *dev)
>> at91_twi_write(dev, AT91_TWI_CR,
>> AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
>> }
>> +
>> + /*
>> + * After timeout, some faulty I2C slave devices might hold
>> SCL/SDA down;
>> + * we can send a bus clear command, hoping that the pins will be
>> + * released
>> + */
>> + if (!(dev->transfer_status & AT91_TWI_SDA) ||
>> + !(dev->transfer_status & AT91_TWI_SCL)) {
>> + dev_dbg(dev->dev,
>> + "SDA/SCL are 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);
>
> This bit is not documented on SoCs before SAMA5D2/D4, this write
> shouldn't be done unconditionally.
>
>
Indeed, they are not present on SAMA5D4 or earlier SoCs. It is supported
on SAMA5D2 though. I will make a new version and implement the CLEAR
command only for the SoCs that support it.
Thank you for your review.
Best regards,
Codrin
