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Subject: Re: [PATCH v2] iio: buffer: Don't allow buffers without any channels
 enabled to be activated
To:     "Ardelean, Alexandru" <alexandru.Ardelean@analog.com>,
        "andy.shevchenko@gmail.com" <andy.shevchenko@gmail.com>
Cc:     "pmeerw@pmeerw.ne" <pmeerw@pmeerw.ne>,
        "jic23@kernel.org" <jic23@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
        "knaack.h@gmx.de" <knaack.h@gmx.de>
References: <20200320104031.31701-1-alexandru.ardelean@analog.com>
 <20200325100112.85107-1-alexandru.ardelean@analog.com>
 <CAHp75VfVggWZ6WhOa=nUrxyd0dJrTbZd9NnUMhQ_S=kncrAhOw@mail.gmail.com>
 <62b90724f16fa3a2c54b7e7f2321587a328d7209.camel@analog.com>
From:   Lars-Peter Clausen <lars@metafoo.de>
Message-ID: <f74263bc-5d42-db67-942e-f5970c71381e@metafoo.de>
Date:   Thu, 26 Mar 2020 08:44:27 +0100
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On 3/26/20 8:42 AM, Ardelean, Alexandru wrote:
> On Wed, 2020-03-25 at 17:57 +0200, Andy Shevchenko wrote:
>> [External]
>>
>> On Wed, Mar 25, 2020 at 12:02 PM Alexandru Ardelean
>> <alexandru.ardelean@analog.com> wrote:
>>> From: Lars-Peter Clausen <lars@metafoo.de>
>>>
>>> Before activating a buffer make sure that at least one channel is enabled.
>>> Activating a buffer with 0 channels enabled doesn't make too much sense and
>>> disallowing this case makes sure that individual driver don't have to add
>>> special case code to handle it.
>>>
>>> Currently, without this patch enabling a buffer is possible and no error is
>>> produced. With this patch -EINVAL is returned.
>>>
>>> An example of execution with this patch and some instrumented print-code:
>>>     root@analog:~# cd /sys/bus/iio/devices/iio\:device3/buffer
>>>     root@analog:/sys/bus/iio/devices/iio:device3/buffer# echo 1 > enable
>>>     0: iio_verify_update 748 indio_dev->masklength 2 *insert_buffer-
>>>> scan_mask 00000000
>>>     1: iio_verify_update 753
>>>     2:__iio_update_buffers 1115 ret -22
>>>     3: iio_buffer_store_enable 1241 ret -22
>>>     -bash: echo: write error: Invalid argument
>>> 1, 2 & 3 are exit-error paths. 0 the first print in iio_verify_update()
>>> rergardless of error path.
>>>
>>> Without this patch (and same instrumented print-code):
>>>     root@analog:~# cd /sys/bus/iio/devices/iio\:device3/buffer
>>>     root@analog:/sys/bus/iio/devices/iio:device3/buffer# echo 1 > enable
>>>     0: iio_verify_update 748 indio_dev->masklength 2 *insert_buffer-
>>>> scan_mask 00000000
>>>     root@analog:/sys/bus/iio/devices/iio:device3/buffer#
>>> Buffer is enabled with no error.
>>>
>>> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
>>> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
>>> ---
>>>
>>> Changelog v1 -> v2:
>>> * moved check in iio_verify_update()
>>> * added dev_dbg() message; should help some folks understand the message
>>> * documented steps to reproduce
>>> * added Fixes tag; hopefully the tag is the good one; if needed, it can be
>>>    dropped; this has been around for ~8 years; no idea if it's worth
>>>    backporting
>> Where?
> stable/fixes/lts-kernels
> don't have a really good clue about where these things need backporting;
What Andy means is that there is no Fixes tag :)