linux-kernel - Re: [PATCH v2] hwmon: Add driver for Gigabyte AORUS Waterforce AIO coolers

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Message-ID: <34638d1a-55c2-4dfe-ab9b-d8591a32b950@roeck-us.net>
Date:   Tue, 5 Dec 2023 06:35:19 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Aleksa Savic <savicaleksa83@...il.com>
Cc:     linux-hwmon@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] hwmon: Add driver for Gigabyte AORUS Waterforce AIO
 coolers

On 12/5/23 06:22, Aleksa Savic wrote:
> On 2023-12-03 18:36:35 GMT+01:00, Guenter Roeck wrote:
>> On Sun, Dec 03, 2023 at 01:06:48PM +0100, Aleksa Savic wrote:
>>> This driver exposes hardware sensors of the Gigabyte AORUS Waterforce
>>> all-in-one CPU liquid coolers, which communicate through a proprietary
>>> USB HID protocol. Report offsets were initially discovered in [1] and
>>> confirmed by me on a Waterforce X240 by observing the sent reports from
>>> the official software.
>>>
>>> Available sensors are pump and fan speed in RPM, as well as coolant
>>> temperature. Also available through debugfs is the firmware version.
>>>
>>> Attaching a fan is optional and allows it to be controlled from the
>>> device. If it's not connected, the fan-related sensors will report
>>> zeroes.
>>>
>>> The addressable RGB LEDs and LCD screen are not supported in this
>>> driver and should be controlled through userspace tools.
>>>
>>> [1]: https://github.com/liquidctl/liquidctl/issues/167
>>>
>>> Signed-off-by: Aleksa Savic <savicaleksa83@...il.com>
>>> ---
...
>>> +static int waterforce_get_status(struct waterforce_data *priv)
>>> +{
>>> +	int ret = 0;
>>> +
>>> +	if (!mutex_lock_interruptible(&priv->status_report_request_mutex)) {
>>> +		if (!time_after(jiffies, priv->updated + msecs_to_jiffies(STATUS_VALIDITY))) {
>>> +			/* Data is up to date */
>>> +			goto unlock_and_return;
>>> +		}
>>
>> What is the point of this check ? The calling code already checks it.
>> Checking it twice, once inside and once outside the lock, seems
>> excessive.
>>
> 
> If there are multiple readers here, only the first one should request the status,
> so when others enter the mutex they can exit early if the data is there.
> 

Please change the code to only check once from within the mutex.

Guenter