linux-kernel - Re: [PATCH v3 10/15] leds: leds-gpio: Add ACPI probing support

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Message-ID: <20141001091309.GY1786@lahna.fi.intel.com>
Date:	Wed, 1 Oct 2014 12:13:09 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	devicetree@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>
Subject: Re: [PATCH v3 10/15] leds: leds-gpio: Add ACPI probing support

On Wed, Oct 01, 2014 at 10:13:04AM +0200, Arnd Bergmann wrote:
> On Wednesday 01 October 2014 04:17:02 Rafael J. Wysocki wrote:
> > Index: linux-pm/drivers/leds/leds-gpio.c
> > ===================================================================
> > --- linux-pm.orig/drivers/leds/leds-gpio.c
> > +++ linux-pm/drivers/leds/leds-gpio.c
> > @@ -231,6 +231,13 @@ static const struct of_device_id of_gpio
> >  
> >  MODULE_DEVICE_TABLE(of, of_gpio_leds_match);
> >  
> > +static const struct acpi_device_id acpi_gpio_leds_match[] = {
> > +       { "PRP0001" }, /* Device Tree shoehorned into ACPI */
> > +       {},
> > +};
> > +
> > +MODULE_DEVICE_TABLE(acpi, acpi_gpio_leds_match);
> > +
> >  static int gpio_led_probe(struct platform_device *pdev)
> >  {
> >         struct gpio_led_platform_data *pdata = dev_get_platdata(&pdev->dev);
> > @@ -286,6 +293,7 @@ static struct platform_driver gpio_led_d
> >                 .name   = "leds-gpio",
> >                 .owner  = THIS_MODULE,
> >                 .of_match_table = of_gpio_leds_match,
> > +               .acpi_match_table = acpi_gpio_leds_match,
> >         },
> >  };
> 
> Is this something you'd have to do in every driver you want to support
> _PRP based probing? For the ".acpi_match_table =" reference, I think
> you could actually provide a generic acpi_device_id table exported from
> core code that you refer to, so each driver just does
> 
> 	.acpi_match_table = acpi_match_by_of_compatible,
> 
> (or whatever you want to call it).

That's a good idea.

> Regarding the MODULE_DEVICE_TABLE, I suspect the above won't work the
> way you are hoping for, because once you get to dozens or hundreds of
> drivers doing this, each device will show up with the same string,
> so udev will try to load all the modules that list "PRP0001". That
> doesn't look right. With the code from patch 3, you can probably drop
> the acpi MODULE_DEVICE_TABLE() entirely and get the correct behavior.

It actually works like this now:

 # cd /sys/bus/platform/devices/PRP0001\:00/
 DRIVER=leds-gpio
 MODALIAS=of:Nprp0001TacpiCgpio-leds

 # cat modalias 
 of:Nprp0001TacpiCgpio-leds

In other words the modalias changes to be of:Nprp0001Tacpi, e.g
name=prp0001, type=acpi and then list of compatible values.

Udev then loads only module that matches the modalias so it should not
load everything listing PRP0001 in their MODULE_DEVICE_TABLE().
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