linux-kernel - Re: [PATCH v5 5/5] hwmon: Add support for Amphenol ChipCap 2

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] [day] [month] [year] [list]

Date: Thu, 18 Jan 2024 17:37:40 +0100
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: Mark Brown <broonie@...nel.org>
Cc: Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Jean Delvare <jdelvare@...e.com>,
 Guenter Roeck <linux@...ck-us.net>, Jonathan Corbet <corbet@....net>,
 Liam Girdwood <lgirdwood@...il.com>, Rob Herring <robh@...nel.org>,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 5/5] hwmon: Add support for Amphenol ChipCap 2


On 18.01.24 17:04, Mark Brown wrote:
> On Thu, Jan 18, 2024 at 04:30:37PM +0100, Javier Carrasco wrote:
>> On 18.01.24 14:49, Mark Brown wrote:
>>> On Mon, Jan 15, 2024 at 09:02:25PM +0100, Javier Carrasco wrote:
> 
>>>> +static int cc2_enable(struct cc2_data *data)
>>>> +{
>>>> +	int ret;
> 
>>>> +	if (regulator_is_enabled(data->regulator))
>>>> +		return 0;
> 
>>> This is generally a sign that the regulator API usage is not good, the
>>> driver should not rely on references to the regulator held by anything
>>> else since whatever else is holding the regulator on could turn it off
>>> at any time.  If the driver did the enable itself then it should know
>>> that it did so and not need to query.
> 
>> The driver handles a dedicated regulator, but I wanted to account for
>> the cases where the attempts to enable and disable the regulator fail
>> and keep parity. If the disabling attempt fails, will the regulator not
>> stay enabled? In that case, an additional call to regulator_enable would
>> not be required, right?
>> That is the only reason I am using regulator_is_enabled(), but maybe
>> things don't work like that.
> 
> With exclusive use you can get away with this, you should have a comment
> for that case though.
> 
I will add a comment to clarify it.
>>>> +	ret = regulator_enable(data->regulator);
>>>> +	if (ret < 0)
>>>> +		return ret;
>>>> +
>>>> +	/*
>>>> +	 * TODO: the startup-delay-us property of the regulator might be
>>>> +	 * added to the delay (if provided).
>>>> +	 * Currently there is no interface to read its value apart from
>>>> +	 * a direct access to regulator->rdev->constraints->enable_time,
>>>> +	 * which is discouraged like any direct access to the regulator_dev
>>>> +	 * structure. This would be relevant in cases where the startup delay
>>>> +	 * is in the range of milliseconds.
>>>> +	 */
>>>> +	usleep_range(CC2_STARTUP_TIME_US, CC2_STARTUP_TIME_US + 125);
> 
>>> Note that the regulator startup delay is the time taken for the
>>> regulator to power up so if the device needs additional delay then that
>>> will always need to be in addition to whatever the regulator is doing.
> 
>> What I mean by that is that the device cannot be ready until the
>> regulator powers it up (obvious) plus the start up time of the device
>> itself once it gets powered up. So if a regulator takes for example 1 ms
>> to power up, the sleep function could (and should) wait for 1 ms longer.
> 
> No, the sleep function should do nothing of the sort - if any delay is
> neeeded for the regulator it will be handled as part of enabling the
> regulator.  This is not exposed to client drivers because it is
> transparent to them.
That sounds great. Then there is no need for the comment altogether and
the TODO will go away.

Thank you again and best regards,
Javier Carrrasco