Re: [PATCH 03/16] iio: adc: at91-sama5d2_adc: exit from write_raw() when buffers are enabled

Claudiu.Beznea
2022-06-14T08:19:55Z

On 11.06.2022 20:33, Jonathan Cameron wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>
> On Thu, 9 Jun 2022 11:32:00 +0300
> Claudiu Beznea <claudiu.beznea@microchip.com> wrote:
>
>> When buffers are enabled conversion may start asynchronously thus
>> allowing changes on actual hardware could lead to bad behavior. Thus
>> do not allow changing oversampling ratio and sample frequency when
>> buffers are enabled.
>
> Less than desirable behavior perhaps, but broken? I don't see this
> as a fix from what you have mentioned - though I'm not against it.
> (just drop the fixes tag)
> It is an ABI change, but unlikely to be one any sane code hits.
>
>>
>> Fixes: 5e1a1da0f8c9 ("iio: adc: at91-sama5d2_adc: add hw trigger and buffer support")
>> Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
>> ---
>> drivers/iio/adc/at91-sama5d2_adc.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
>> index a672a520cdc0..b76328da0cb2 100644
>> --- a/drivers/iio/adc/at91-sama5d2_adc.c
>> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
>> @@ -1644,6 +1644,9 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
>> {
>> struct at91_adc_state *st = iio_priv(indio_dev);
>>
>> + if (iio_buffer_enabled(indio_dev))
>> + return -EBUSY;
>
> This is racy as nothing stops buffers being enabled after this point.
> Use the iio_device_claim_direct_mode() and release for this as they
> protect against the race.

OK, thanks!

>
>
>> +
>> switch (mask) {
>> case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
>> if ((val != AT91_OSR_1SAMPLES) && (val != AT91_OSR_4SAMPLES) &&
>