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

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Date:	Tue, 31 May 2016 15:20:18 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Jonathan Cameron <jic23@...nel.org>,
	Daniel Baluta <daniel.baluta@...il.com>,
	Alison Schofield <amsfield22@...il.com>
Cc:	"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 05/29/2016 07:06 PM, 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.

It will only be locked once. sysfs_streq() will only match for a single
item. But you are right the code could be refactored to make that more
clearer. First run the lookup look and then apply afterwards.