linux-kernel - Re: [PATCH v2 4/4] platform/x86: topstar-laptop: add optional WLAN LED workaround

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Date:   Sun, 5 Nov 2017 14:34:43 -0800
From:   Darren Hart <dvhart@...radead.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Guillaume Douézan-Grard 
        <gdouezangrard@...il.com>, Andy Shevchenko <andy@...radead.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] platform/x86: topstar-laptop: add optional WLAN
 LED workaround

On Sun, Nov 05, 2017 at 03:28:09PM +0200, Andy Shevchenko wrote:
> On Fri, Nov 3, 2017 at 5:07 PM, Guillaume Douézan-Grard
> <gdouezangrard@...il.com> wrote:
> > On Fri, Nov 03, 2017 at 02:50:52PM +0200, Andy Shevchenko wrote:
> >> On Sun, Oct 29, 2017 at 1:53 AM, Guillaume Douézan-Grard
> >> <gdouezangrard@...il.com> wrote:
> >> > Topstar U931 laptops provide an LED synced with the WLAN adapter
> >> > hard-blocking state. Unfortunately, some models seem to be defective,
> >> > making impossible to hard-block the adapter with the WLAN switch and
> >> > thus the LED is useless.
> >> >
> >> > An ACPI method is available to programmatically control this switch and
> >> > it indirectly allows to control the LED.
> >> >
> >> > This commit registers the LED within the corresponding subsystem, making
> >> > possible for instance to use an rfkill-based trigger to synchronize the
> >> > LED with the soft-blocking state.
> >> >
> >> > This feature is disabled by default and can be enabled with the
> >> > `led_workaround` module parameter.
> >>
> >> >  #include <linux/platform_device.h>
> >> >  #include <linux/input.h>
> >> >  #include <linux/input/sparse-keymap.h>
> >> > +#include <linux/leds.h>
> >>
> >> Yep, exact place, esp. after moving platform_device to the right place.
> >>
> >> > +static bool led_workaround;
> >> > +module_param_named(led_workaround, led_workaround, bool, 0444);
> >> > +MODULE_PARM_DESC(led_workaround,
> >> > +               "Enables software-based WLAN LED control on systems with defective hardware switch");
> >>
> >> So, this is most problematic piece in the series.
> >>
> >> We are not encouraging module parameters. Why do we need one? Can't be
> >> detected automatically (perhaps based on DMI strings)?
> >
> > Darren told me that.
> 
> > I tried to answer this question in the cover letter:
> 
> Perhaps it makes sense to put this explanation in the commit message.
> 
> > "These are barebone laptops, sold under quite a lot of brands and
> > configurations, with different firmwares and so on. I can only say for sure
> > that this issue is present for all the models sold under a specific brand,
> > that's why I'm reluctant to enable this by default with a DMI check."
> >
> > In my case for instance, the DMI info has not been filled in by the retailler
> > since I only have the ODM base board information to identify a model.
> 
> I see. I would like to have a consensus on this one with Darren, the
> rest (after addressing comments) looks good to me.

If you can definitively say that all models of brand X and this HID have this
quirk, that is considerably better than a lot of quirks we deal with today. I
suggest doing that and holding off on the option. If it gets to the point where
a number otherwise unidentifiable systems have this problem, we can add the
option then.

-- 
Darren Hart
VMware Open Source Technology Center