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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Wed, 25 Mar 2020 17:57:50 +0200
Message-ID: <CAHp75VfVggWZ6WhOa=nUrxyd0dJrTbZd9NnUMhQ_S=kncrAhOw@mail.gmail.com>
Subject: Re: [PATCH v2] iio: buffer: Don't allow buffers without any channels
 enabled to be activated
To:     Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc:     linux-iio <linux-iio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Hartmut Knaack <knaack.h@gmx.de>,
        Peter Meerwald <pmeerw@pmeerw.ne>
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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?

>
>  drivers/iio/industrialio-buffer.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 5ff34ce8b6a2..e6fa1a4e135d 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -686,6 +686,13 @@ static int iio_verify_update(struct iio_dev *indio_dev,
>         bool scan_timestamp;
>         unsigned int modes;
>
> +       if (insert_buffer &&
> +           bitmap_empty(insert_buffer->scan_mask, indio_dev->masklength)) {
> +               dev_dbg(&indio_dev->dev,
> +                       "At least one scan element must be enabled first\n");
> +               return -EINVAL;
> +       }
> +
>         memset(config, 0, sizeof(*config));
>         config->watermark = ~0;
>
> --
> 2.17.1
>


-- 
With Best Regards,
Andy Shevchenko