linux-kernel - Re: [PATCH v2] iio: buffer: Don't allow buffers without any channels enabled to be activated

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Message-ID: <7f131ff7c29fe36f56dc2892945d7a7d9c63b433.camel@analog.com>
Date:   Thu, 26 Mar 2020 07:46:44 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        "lars@...afoo.de" <lars@...afoo.de>
CC:     "pmeerw@...erw.ne" <pmeerw@...erw.ne>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "knaack.h@....de" <knaack.h@....de>
Subject: Re: [PATCH v2] iio: buffer: Don't allow buffers without any channels
 enabled to be activated

On Thu, 2020-03-26 at 08:44 +0100, Lars-Peter Clausen wrote:
> [External]
> 
> 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@...log.com> wrote:
> > > > From: Lars-Peter Clausen <lars@...afoo.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@...log:~# cd /sys/bus/iio/devices/iio\:device3/buffer
> > > >     root@...log:/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@...log:~# cd /sys/bus/iio/devices/iio\:device3/buffer
> > > >     root@...log:/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@...log:/sys/bus/iio/devices/iio:device3/buffer#
> > > > Buffer is enabled with no error.
> > > > 
> > > > Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> > > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.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 :)

oh crap....
i added one but seem to have lost it when moving the patch to the server from
where i do git-send
i'll add one;