linux-kernel - Re: [PATCH v4] HID: i2c-hid: add polling mode based on connected GPIO chip's pin status

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Date:   Wed, 9 Dec 2020 16:44:35 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Barnabás Pőcze <pobrn@...tonmail.com>
Cc:     Coiby Xu <coiby.xu@...il.com>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        Helmut Stult <helmut.stult@...info.de>,
        Baq Domalaq <domalak@...il.com>,
        Pedro Ribeiro <pedrib@...il.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] HID: i2c-hid: add polling mode based on connected
 GPIO chip's pin status

On Wed, Dec 09, 2020 at 03:38:11PM +0000, Barnabás Pőcze wrote:
> 2020. december 9., szerda 8:00 keltezéssel, Greg KH írta:
> 
> > On Tue, Dec 08, 2020 at 09:59:20PM +0000, Barnabás Pőcze wrote:
> >
> > > 2020.  november 25., szerda 16:07 keltezéssel, Greg KH írta:
> > >
> > > > [...]
> > > >
> > > > > +static u8 polling_mode;
> > > > > +module_param(polling_mode, byte, 0444);
> > > > > +MODULE_PARM_DESC(polling_mode, "How to poll (default=0) - 0 disabled; 1 based on GPIO pin's status");
> > > >
> > > > Module parameters are for the 1990's, they are global and horrible to
> > > > try to work with. You should provide something on a per-device basis,
> > > > as what happens if your system requires different things here for
> > > > different devices? You set this for all devices :(
> > > > [...]
> > >
> > > Hi
> > > do you think something like what the usbcore has would be better?
> > > A module parameter like "quirks=<vendor-id>:<product-id>:<flags>[,<vendor-id>:<product-id>:<flags>]*"?
> >
> > Not really, that's just for debugging, and asking users to test
> > something, not for a final solution to anything.
> 
> My understanding is that this polling mode option is by no means intended
> as a final solution, it's purely for debugging/fallback:
> 
> "Polling mode could be a fallback solution for enthusiastic Linux users
> when they have a new laptop. It also acts like a debugging feature. If
> polling mode works for a broken touchpad, we can almost be certain
> the root cause is related to the interrupt or power setting."
> 
> What would you suggest instead of the module parameter?

a debugfs file?  That means it's only for debugging and you have to be
root to change the value.

thanks,

greg k-h