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SubjectRe: [PATCH] i2c: at91: Send bus clear command if SCL or SDA is down
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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@microchip.com>
> ---
> 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.


--
Kamel Bouhara, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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