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Date:   Sat, 21 Oct 2023 19:03:15 +0300
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Subject: Re: [PATCH v2 0/2] Sanity-check available_scan_masks array
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To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
        Lars-Peter Clausen <lars@metafoo.de>,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
References: <cover.1697452986.git.mazziesaccount@gmail.com>
 <20231021165535.34dcb94b@jic23-huawei>
From:   Matti Vaittinen <mazziesaccount@gmail.com>
In-Reply-To: <20231021165535.34dcb94b@jic23-huawei>
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On 10/21/23 18:55, Jonathan Cameron wrote:
> On Mon, 16 Oct 2023 14:04:11 +0300
> Matti Vaittinen <mazziesaccount@gmail.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.

Makes perfect sense to me.

>  I'll aim to pick it up early
> in next cycle. Give me a poke if I still haven't by rc3 or so.

Ouch... My memory gets worse year by year - well, I'll try to remember :)

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~