linux-kernel - Re: [PATCH v4 07/10] iio: adc: ti-ads7924: Respect device tree config

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d391b012-0a8e-40ca-af56-ca73b3fd853b@gmail.com>
Date: Wed, 26 Feb 2025 08:39:11 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: David Lechner <dlechner@...libre.com>,
 Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
 Hugo Villeneuve <hvilleneuve@...onoff.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen
 <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Daniel Scally <djrscally@...il.com>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>,
 Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
 Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Samuel Holland <samuel@...lland.org>,
 Hugo Villeneuve <hvilleneuve@...onoff.com>, Nuno Sa <nuno.sa@...log.com>,
 Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Guillaume Stols <gstols@...libre.com>,
 Olivier Moysan <olivier.moysan@...s.st.com>,
 Dumitru Ceclan <mitrutzceclan@...il.com>,
 Trevor Gamblin <tgamblin@...libre.com>,
 Matteo Martelli <matteomartelli3@...il.com>,
 Alisa-Dariana Roman <alisadariana@...il.com>,
 Ramona Alexandra Nechita <ramona.nechita@...log.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v4 07/10] iio: adc: ti-ads7924: Respect device tree config

On 26/02/2025 02:09, David Lechner wrote:
> On 2/24/25 12:34 PM, Matti Vaittinen wrote:
>> The ti-ads7924 driver ignores the device-tree ADC channel specification
>> and always exposes all 4 channels to users whether they are present in
>> the device-tree or not. Additionally, the "reg" values in the channel
>> nodes are ignored, although an error is printed if they are out of range.
>>
>> Register only the channels described in the device-tree, and use the reg
>> property as a channel ID.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
>>
>> ---
>> Revision history:
>> v3 => v4:
>>   - Adapt to 'drop diff-channel support' changes to ADC-helpers
>>   - select ADC helpers in the Kconfig
>> v2 => v3: New patch
>>
>> Please note that this is potentially breaking existing users if they
>> have wrong values in the device-tree. I believe the device-tree should
>> ideally be respected, and if it says device X has only one channel, then
>> we should believe it and not register 4. Well, we don't live in the
>> ideal world, so even though I believe this is TheRightThingToDo - it may
>> cause havoc because correct device-tree has not been required from the
>> day 1. So, please review and test and apply at your own risk :)
> 
> The DT bindings on this one are a little weird. Usually, if we don't
> use any extra properties from adc.yaml, we leave out the channels. In
> this case it does seem kind of like the original intention was to work
> like you are suggesting, but hard to say since the driver wasn't actually
> implemented that way. I would be more inclined to actually not make the
> breaking change here and instead relax the bindings to make channel nodes
> optional and just have the driver ignore the channel nodes by dropping
> the ads7924_get_channels_config() function completely. This would make
> the driver simpler instead of more complex like this patch does.

I have no strong opinion on this. I see this driver says 'Supported' in 
MAINTAINERS. Maybe Hugo is able to provide some insight?

>> As a side note, this might warrant a fixes tag but the adc-helper -stuff
>> is hardly worth to be backported... (And I've already exceeded my time
>> budget with this series - hence I'll leave crafting backportable fix to
>> TI people ;) )
>>
>> This has only been compile tested! All testing is highly appreciated.
>> ---
> 
> ...
> 
>> -static int ads7924_get_channels_config(struct device *dev)
>> +static int ads7924_get_channels_config(struct iio_dev *indio_dev,
>> +				       struct device *dev)
> 
> Could get dev from indio_dev->dev.parent and keep only one parameter
> to this function.
> 
>>   {
>> -	struct fwnode_handle *node;
>> -	int num_channels = 0;
>> +	struct iio_chan_spec *chan_array;
>> +	int num_channels = 0, i;
> 
> Don't need initialization here.
> 
>> +	static const char * const datasheet_names[] = {
>> +		"AIN0", "AIN1", "AIN2", "AIN3"
>> +	};

Thanks for the review David! I do agree with the comments to the code.

Yours,
	-- Matti