linux-kernel - Re: [PATCH 03/16] iio: adc: at91-sama5d2_adc: exit from write

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Date:   Tue, 14 Jun 2022 08:19:44 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <jic23@...nel.org>
CC:     <Eugen.Hristev@...rochip.com>, <lars@...afoo.de>,
        <Nicolas.Ferre@...rochip.com>, <alexandre.belloni@...tlin.com>,
        <robh+dt@...nel.org>, <krzk+dt@...nel.org>,
        <ludovic.desroches@...el.com>, <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/16] iio: adc: at91-sama5d2_adc: exit from write_raw()
 when buffers are enabled

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@...rochip.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@...rochip.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) &&
>