linux-kernel - Re: [PATCH 2/7] iio: adc: ad7791: claim direct mode when writing frequency

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Message-ID: <a349082f-89c4-7e01-2cc4-7136234acbff@kernel.org>
Date:	Sun, 29 May 2016 18:07:41 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Daniel Baluta <daniel.baluta@...il.com>,
	Alison Schofield <amsfield22@...il.com>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	"Hennerich, Michael" <Michael.Hennerich@...log.com>,
	Hartmut Knaack <knaack.h@....de>,
	Peter Meerwald-Stadler <pmeerw@...erw.net>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/7] iio: adc: ad7791: claim direct mode when writing
 frequency

On 29/05/16 18:06, Jonathan Cameron wrote:
> On 25/05/16 11:34, Daniel Baluta wrote:
>> On Tue, May 24, 2016 at 10:16 PM, Alison Schofield <amsfield22@...il.com> wrote:
>>> Driver was checking for direct mode and trying to lock it, but
>>> left a gap where mode could change before the desired operation.
>>> Use iio_device_claim_direct_mode() to guarantee device stays in
>>> direct mode.
>>>
>>> Signed-off-by: Alison Schofield <amsfield22@...il.com>
>>> Cc: Daniel Baluta <daniel.baluta@...il.com>
>>
>> Looks good to me. We could use an Acked-by from Lars here.
>>
>> Acked-by: Daniel Baluta <daniel.baluta@...il.com>
> This one is a little more interesting.  I wonder if we wouldn't be better
> off taking the lock for the whole function rather than dropping it for
> short periods.
> 
> Can apply such a change at a later date however.
> 
> Applied to the togreg branch of iio.git - initially pushed out as testing
> for the autobuilders to play with it.
Actually haven't seen Daniel suggesting an Ack from Lars might be good for this
one I've backed it out for now.

Lars?
> 
> Thanks,
> 
> Jonathan
> 
>>
>>> ---
>>>  drivers/iio/adc/ad7791.c | 15 ++++-----------
>>>  1 file changed, 4 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/iio/adc/ad7791.c b/drivers/iio/adc/ad7791.c
>>> index cf172d58..f7edacc 100644
>>> --- a/drivers/iio/adc/ad7791.c
>>> +++ b/drivers/iio/adc/ad7791.c
>>> @@ -272,24 +272,17 @@ static ssize_t ad7791_write_frequency(struct device *dev,
>>>         struct ad7791_state *st = iio_priv(indio_dev);
>>>         int i, ret;
>>>
>>> -       mutex_lock(&indio_dev->mlock);
>>> -       if (iio_buffer_enabled(indio_dev)) {
>>> -               mutex_unlock(&indio_dev->mlock);
>>> -               return -EBUSY;
>>> -       }
>>> -       mutex_unlock(&indio_dev->mlock);
>>> -
>>> -       ret = -EINVAL;
>>> -
>>>         for (i = 0; i < ARRAY_SIZE(ad7791_sample_freq_avail); i++) {
>>>                 if (sysfs_streq(ad7791_sample_freq_avail[i], buf)) {
>>>
>>> -                       mutex_lock(&indio_dev->mlock);
>>> +                       ret = iio_device_claim_direct_mode(indio_dev);
>>> +                       if (ret)
>>> +                               return ret;
>>>                         st->filter &= ~AD7791_FILTER_RATE_MASK;
>>>                         st->filter |= i;
>>>                         ad_sd_write_reg(&st->sd, AD7791_REG_FILTER,
>>>                                          sizeof(st->filter), st->filter);
>>> -                       mutex_unlock(&indio_dev->mlock);
>>> +                       iio_device_release_direct_mode(indio_dev);
>>>                         ret = 0;
>>>                         break;
>>>                 }
>>> --
>>> 2.1.4
>>>
>>> --
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> 
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