From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Jones Subject: Re: [PATCH 1/5] capemgr: Beaglebone DT overlay based cape manager Date: Tue, 8 Jan 2013 10:48:32 +0000 Message-ID: <20130108104832.GE21994@gmail.com> References: <1357584666-17374-1-git-send-email-panto@antoniou-consulting.com> <93BF5C62-ADE8-4EFC-9175-C2D7E43300E3@antoniou-consulting.com> <20130107210551.GL14149@atomide.com> <201301072135.05166.arnd@arndb.de> <89A7A8FD-935E-4225-8C7B-EA1DBA0C2780@antoniou-consulting.com> <20130108100042.GD21994@gmail.com> <21E7B891-269B-422D-9038-381FAA15B59B@antoniou-consulting.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <21E7B891-269B-422D-9038-381FAA15B59B@antoniou-consulting.com> Sender: linux-doc-owner@vger.kernel.org To: Pantelis Antoniou Cc: Arnd Bergmann , Tony Lindgren , Grant Likely , Rob Herring , Rob Landley , Jon Loeliger , Stephen Warren , David Gibson , Benoit Cousson , Mitch Bradley , Alan Tull , Greg Kroah-Hartman , linux-omap@vger.kernel.org, devicetree-discuss@lists.ozlabs.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Matt Porter , Russ Dill , Koen Kooi , Joel A Fernandes , Rob Clark , Jason Kridner , Matt Ranostay , Sascha Hauer , Linus Walleij List-Id: linux-omap@vger.kernel.org On Tue, 08 Jan 2013, Pantelis Antoniou wrote: > Hi Lee, >=20 > On Jan 8, 2013, at 12:00 PM, Lee Jones wrote: >=20 > >>>>> At the end of the line, some kind of hardware glue is going to = be needed. > >>>>>=20 > >>>>> 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 makin= g it overly > >>>>> general, besides the part that are obviously part of the infras= tructure=20 > >>>>> (like the DT overlay stuff). > >>>>>=20 > >>>>> 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.=20 > >>>>=20 > >>>> 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 framewo= rk and > >>>> so on. > >>>>=20 > >>>> So I suggest a minimal generic API from the start as that will m= ake things > >>>> a lot easier in the long run. > >>>=20 > >>> I agree. The ux500 platform already has the concept of "user inte= rface boards", > >>> which currently is not well integrated into devicetree. I believe= Sascha > >>> mentioned that Pengutronix had been shipping some other systems w= ith add-on > >>> boards and generating device tree binaries from source for each c= ombination. > >>>=20 > >>> Ideally, both of the above should be able to use the same DT over= lay logic > >>> as BeagleBone, and I'm sure there are more of those. > >>=20 > >> Hmm, I see.=20 > >>=20 > >> 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 tho= se boards, etc. > >=20 > > User Interface Boards are mearly removable PCBs which are interchan= geable > > 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. > >=20 > > You can find a small example of how we interface to these by viewin= g > > '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. >=20 > I see. What I'm asking about is whether there's a method where you ca= n read > an EEPROM, or some GPIO code combination where I can find out what ki= nd of board > is plugged each time. >=20 > 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. Unfortunately, there is no way to probe the UIBs. :( > >> Can we get some input by the owner of other similar hardware? I kn= ow the FPGA > >> people have similar requirements for example. There are other peop= le that are hitting > >> problems getting DT to work with their systems, like the V4L peopl= e with the order > >> of initialization; see http://lwn.net/Articles/531068/. I think th= e V4L problem is > >> cleanly solved by the overlay being contained in the V4L device no= de and applied just before > >> the device is probed. > >>=20 > >> In the meantime it would be better to wait until we have some ack = from the maintainers > >> of the core subsystems about what they think. --=20 Lee Jones Linaro ST-Ericsson Landing Team Lead Linaro.org =E2=94=82 Open source software for ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog