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

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Date:	Wed, 1 Oct 2014 17:04:41 +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 03:52:42PM +0200, Arnd Bergmann wrote:
> On Wednesday 01 October 2014 14:59:01 Mika Westerberg wrote:
> > On Wed, Oct 01, 2014 at 12:01:34PM +0200, Arnd Bergmann wrote:
> > > On Wednesday 01 October 2014 12:13:09 Mika Westerberg wrote:
> > > > 
> > > > > 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().
> > > 
> > > I'm not completely following yet. I can see how this works now, but
> > > how is this better than just using the existing modalias for OF?
> > 
> > You mean using just what of_device_get_modalias() would create? In that
> > case, what do we put to name and type fields?
> 
> Sorry, I think we're still both misunderstanding one another. You were
> talking about the modalias created by the device scanning above, while
> I meant the one in the MODULE_DEVICE_TABLE. 

Right, got it now.

> With the entry you create in create_modalias(), you will only ever
> match against the MODULE_DEVICE_TABLE(of, of_gpio_leds_match)
> line, not against the MODULE_DEVICE_TABLE(acpi, acpi_gpio_leds_match),
> so I think you can just drop the latter.

Indeed.

> On the question what to put into the name and type fields, that is
> unrelated. The type is supposed to be for the 'device_type' property
> in DT, which we should never rely on in a driver that supports both
> APCI and DT. In Linux we only use that for "pci", "cpu" and "memory",
> all of which have their own way of getting probed in ACPI.
> The "name" is normally ignored in DT as well, except for backwards
> compatibility with old bindings, but I would argue that you should not
> just put "prp0001" in there. Either leave it empty like type, or use
> the name of the device as it appears in the ACPI tables, such as "DEV0"
> or "PWM".

OK, I think it makes sense to leave them empty. I remember I tried that
at some point but it didn't work without N and T fields. Is there some
example what to put there in case of empty?

Something like "of:N*T*Cgpio-leds" perhaps?
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