linux-kernel - Re: [PATCH 1/5] capemgr: Beaglebone DT overlay based cape manager

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Date:	Tue, 26 Mar 2013 11:40:58 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Pantelis Antoniou <panto@...oniou-consulting.com>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Tony Lindgren <tony@...mide.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>, Jon Loeliger <jdl@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	David Gibson <david@...son.dropbear.id.au>,
	Benoit Cousson <b-cousson@...com>,
	Mitch Bradley <wmb@...mworks.com>,
	Alan Tull <atull@...era.com>, linux-omap@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Matt Porter <mporter@...com>,
	Russ Dill <Russ.Dill@...com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Joel A Fernandes <agnel.joel@...il.com>,
	Rob Clark <robdclark@...il.com>,
	Jason Kridner <jkridner@...gleboard.org>,
	Matt Ranostay <mranostay@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [PATCH 1/5] capemgr: Beaglebone DT overlay based cape manager

On Tue, Mar 26, 2013 at 04:16:10PM +0000, Grant Likely wrote:
> On Tue, 8 Jan 2013 12:10:20 +0200, Pantelis Antoniou <panto@...oniou-consulting.com> wrote:
> > Hi Lee,
> > 
> > On Jan 8, 2013, at 12:00 PM, Lee Jones wrote:
> > 
> > >>>>> At the end of the line, some kind of hardware glue is going to be needed.
> > >>>>> 
> > >>>>> I just feel that drawing from a sample size of 1 (maybe 2 if I get to throw
> > >>>>> in the beagleboard), it is a bit premature to think about making it overly
> > >>>>> general, besides the part that are obviously part of the infrastructure 
> > >>>>> (like the DT overlay stuff).
> > >>>>> 
> > >>>>> What I'm getting at, is that we need some user experience about this, before
> > >>>>> going away and creating structure out of possible misconception about the uses. 
> > >>>> 
> > >>>> IMHO stuff like this will be needed by many SoCs. Some examples of similar
> > >>>> things for omaps that have eventually become generic frameworks have been
> > >>>> the clock framework, USB OTG support, runtime PM, pinmux framework and
> > >>>> so on.
> > >>>> 
> > >>>> So I suggest a minimal generic API from the start as that will make things
> > >>>> a lot easier in the long run.
> > >>> 
> > >>> I agree. The ux500 platform already has the concept of "user interface boards",
> > >>> which currently is not well integrated into devicetree. I believe Sascha
> > >>> mentioned that Pengutronix had been shipping some other systems with add-on
> > >>> boards and generating device tree binaries from source for each combination.
> > >>> 
> > >>> Ideally, both of the above should be able to use the same DT overlay logic
> > >>> as BeagleBone, and I'm sure there are more of those.
> > >> 
> > >> Hmm, I see. 
> > >> 
> > >> I will need some more information about the interface of the 'user interface boards'.
> > >> I.e. how is the board identified, what is typically present on those boards, etc.
> > > 
> > > User Interface Boards are mearly removable PCBs which are interchangeable
> > > amongst various hardware platforms. They are connected via numerous
> > > connectors which carry all sorts of different data links; i2c, spi, rs232,
> > > etc. The UIB I'm looking at right now has a touchscreen, speakers, a key
> > > pad, leds, jumpers, switches and a bunch of sensors.
> > > 
> > > You can find a small example of how we interface to these by viewing
> > > 'arch/arm/boot/dts/stuib.dtsi'. To add a UIB to a particular build, we
> > > currently include it as a *.dtsi from a platform's dts file.
> > 
> > I see. What I'm asking about is whether there's a method where you can read
> > an EEPROM, or some GPIO code combination where I can find out what kind of board
> > is plugged each time.
> > 
> > If there is not, there is no way to automatically load the overlays; you can always
> > use the kernel command line, or have the a user space application to request the loading
> > of a specific board's overlay.
> > 
> 
> In this case the best thing to do is announce the availability of the
> expansion via a request_firmware() call and let udev handle supplying
> the correct overlay file.

The code to load firmware files was recently removed from udev, now that
the kernel handles this automatically itself :)

But yes, the same call still applies, request_firmware() should work
fine here.

thanks,

greg k-h
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