Re: [PATCH AUTOSEL 4.4 23/60] iio: buffer: Don't allow buffers without any channels enabled to be activated

[Sasha Levin <sashal@kernel.org>]

On Fri, Jun 19, 2020 at 05:27:33PM +0100, Jonathan Cameron wrote:
>On Wed, 17 Jun 2020 21:29:27 -0400
>Sasha Levin <sashal@kernel.org> wrote:
>
>> From: Lars-Peter Clausen <lars@metafoo.de>
>>
>> [ Upstream commit b7329249ea5b08b2a1c2c3f24a2f4c495c4f14b8 ]
>>
>> 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.
>>
>> Note from Jonathan: Probably not suitable for automatic application to stable.
>> This has been there from the very start.  It tidies up an odd corner
>> case but won't effect any 'real' users.
>>
>
>As noted. I don't think it matters if we do apply this to stable.
>It closes an interface oddity rather than an actual known bug.

I'll drop it, thanks!

-- 
Thanks,
Sasha