linux-kernel - Re: [PATCH] hwmon: corsair-cpro: Change to hid driver

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Message-ID: <20200715144441.GC201840@roeck-us.net>
Date:   Wed, 15 Jul 2020 07:44:41 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Marius Zachmann <mail@...iuszachmann.de>
Cc:     Jean Delvare <jdelvare@...e.com>, Jonathan Corbet <corbet@....net>,
        linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: corsair-cpro: Change to hid driver

On Wed, Jul 15, 2020 at 08:59:52AM +0200, Marius Zachmann wrote:
> On 15.07.20 at 04:36:22 CEST, Guenter Roeck wrote
> > On Tue, Jul 14, 2020 at 12:52:30PM +0200, Marius Zachmann wrote:
> > > I found a project which uses hidraw to communicate with the device.
> > > Because I do not want to break any existing userspace code, I
> > > changed this to a hid driver, so hidraw can still be used.
> > > Do I need to include the hid maintainers for the undo in hid-quirks?
> > > 
> > That changelog needs some improvements. It should state what change
> > was made, and why, but not include any questions or personal statements
> > such as "I found ...".
> > 
> > You never really explained why you had changed the driver from hid to
> > usb. Maybe you can explain that decision now ?
> > 
> > Thanks,
> > Guenter
> > 
> 
> This device does not use numbered hid input reports. As far as I know
> it is not possible to determine from which command a response was
> requested. This being a usb driver would not allow any other driver
> to send data to the device.
> In the first (hid) version I did not use hid reports and got
> the usb_device directly from the hid_device which is not intended.
> In this version, requests are made via hid_hw_output_report, waited
> for and received via raw_event.
> If one uses hidraw and this driver at the same time, it still could
> be possible to get switched responses but there is nothing I can
> do about it, as far as I know. This is only about giving the
> possibility to unload the driver and using a userspace driver
> if one chooses.
> 
What a mess. Can you add some of this as comment to the top of the driver
to explain the reasoning ?

Thanks,
Guenter