linux-kernel - Re: [PATCH v2 0/2] Sanity-check available_scan

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Date:   Sat, 21 Oct 2023 16:55:35 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Sanity-check available_scan_masks array

On Mon, 16 Oct 2023 14:04:11 +0300
Matti Vaittinen <mazziesaccount@...il.com> wrote:

> Sanity-check available_scan_masks array
> 
> The available_scan_masks is an array of bitmasks representing the
> channels which can be simultaneously(*) scanned by a driver from the
> device. Following special characteristics apply:
> 
> - When IIO is scanning through the array it will use the first mask
>   which can be used to scan all enabled channels. This means drivers
>   should order the array in the order of the preference. This does also
>   mean that a mask which is a subset of a mask located earler in array
>   will never be used because the earlier one will be picked by the core.
> - Masks wider than size of long are supported only to some extent. The
>   code scanning through the array will interpret the first mask with
>   first long zeroed as end-of-array terminator. Changing this behaviour
>   would make mask-arrays for multi-long masks to be terminated by more
>   than one zero long. Failure to do so would result kernel to read
>   beyond the array generating a potentially hazardous bug.
> 
> Add a sanity-check to IIO-device registration emitting a warning if
> available_scan_mask array is misordered or if mask width is larger than
> a long while available_scan_mask-array is populated. Currently there
> should be no in-tree drivers with available_scan_mask populated and mask
> wider than a long.
> 
> Revision history:
> v1 => v2:
> 	- Add patch 2/2 documenting why iio_scan_mask_match() checks only
> 	  a long worth of bits while searching for the end of the
> 	  available_scan_mask-array.
> 	- Styling of patch 1/2 as per comments from Jonathan
> 	v1 and related discussion here:
> 	https://lore.kernel.org/lkml/ZRvjuZaQWdZw1U1I@dc78bmyyyyyyyyyyyyydt-3.rev.dnainternet.fi/
> 
> Matti Vaittinen (2):
>   iio: sanity check available_scan_masks array
>   iio: buffer: document known issue
> 
>  drivers/iio/industrialio-buffer.c | 16 ++++++++
>  drivers/iio/industrialio-core.c   | 63 +++++++++++++++++++++++++++++++
>  2 files changed, 79 insertions(+)
> 

Hi Matti,

Just a quick note to say this looks fine to me, but I don't want to queue it up
just yet given proximity to merge window etc.  I'll aim to pick it up early
in next cycle. Give me a poke if I still haven't by rc3 or so.

Thanks,

Jonathan