On Mon, 15 Aug 2022 09:16:47 +0000
Denys Zagorui <dzagorui@xxxxxxxxx> wrote:
> From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
>
> After the result of the previous conversion is read the chip
> automatically starts a new conversion and doesn't accept new i2c
> transfers until this conversion is completed which makes the function
> return failure.
That's rather nasty.
Could we add a cheeky sleep in the other path to ensure there is always
time for the conversion to be done? Not ideal, but might ensure
there isn't a known problem path without introducing much complexity.
>
> So add an early return iff the programming of the new address isn't
> needed. Note this will not fix the problem in general, but all cases
> that are currently used. Once this changes we get the failure back, but
> this can be addressed when the need arises.
>
> Fixes: 69548b7c2c4f ("iio: adc: ltc2497: split protocol independent part in a separate module ")
> Reported-by: Meng Li <Meng.Li@xxxxxxxxxxxxx>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Tested-by: Denys Zagorui <dzagorui@xxxxxxxxx>
> ---
> drivers/iio/adc/ltc2497.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
> index f7c786f37ceb..78b93c99cc47 100644
> --- a/drivers/iio/adc/ltc2497.c
> +++ b/drivers/iio/adc/ltc2497.c
> @@ -41,6 +41,19 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
> }
>
> *val = (be32_to_cpu(st->buf) >> 14) - (1 << 17);
> +
> + /*
> + * The part started a new conversion at the end of the above i2c
> + * transfer, so if the address didn't change since the last call
> + * everything is fine and we can return early.
> + * If not (which should only happen when some sort of bulk
> + * conversion is implemented) we have to program the new
> + * address. Note that this probably fails as the conversion that
> + * was triggered above is like not complete yet and the two
> + * operations have to be done in a single transfer.
> + */
> + if (ddata->addr_prev == address)
> + return 0;
> }
>
> ret = i2c_smbus_write_byte(st->client,
