linux-kernel - Re: Hooking up SM501 on TQM5200 (MPC5200) board via device tree?

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Date:	Wed, 8 Jun 2011 09:00:52 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linuxppc-dev@...ts.ozlabs.org, Jamey Sharp <jamey@...ilop.net>
Subject: Re: Hooking up SM501 on TQM5200 (MPC5200) board via device tree?

On Tue, Jun 07, 2011 at 08:09:40PM -0700, Josh Triplett wrote:
> On Fri, Jun 03, 2011 at 02:51:38PM -0600, Grant Likely wrote:
> > On Tue, May 31, 2011 at 10:07:01PM -0700, Josh Triplett wrote:
> > > We have a TQM5200 board, which has GPIO lines hooked up to an SM501.
> > > I've managed to come up with the following patch to the tqm5200 device
> > > tree, which manages to convince the sm501 driver to attach an sm501-fb:
> > > 
> > > --- a/arch/powerpc/boot/dts/tqm5200.dts  2009-11-23 03:13:27.000000000 -0800
> > > +++ b/arch/powerpc/boot/dts/tqm5200.dts  2011-05-31 22:00:28.000580627 -0700
> > > @@ -177,7 +177,8 @@
> > >                 compatible = "fsl,mpc5200-lpb","simple-bus";
> > >                 #address-cells = <2>;
> > >                 #size-cells = <1>;
> > > -               ranges = <0 0 0xfc000000 0x02000000>;
> > > +               ranges = <0 0 0xfc000000 0x02000000
> > > +                         1 0 0xe0000000 0x04000000>;
> > >  
> > >                 flash@0,0 {
> > >                         compatible = "cfi-flash";
> > > @@ -187,6 +188,13 @@
> > >                         #size-cells = <1>;
> > >                         #address-cells = <1>;
> > >                 };
> > > +
> > > +               display@1,0 {
> > > +                       compatible = "smi,sm501";
> > > +                       reg = <1 0x00000000 0x00800000
> > > +                              1 0x03e00000 0x00200000>;
> > > +                       interrupts = <1 1 3>;
> > > +               };
> > >         };
> > >  
> > >         pci@...00d00 {
> > > 
> > > 
> > > However, this doesn't hook up the sm501-gpio bits.  Reading the sm501
> > > driver carefully, it looks like it only hooks up sm501-gpio if it has
> > > platform_data available which sets some flags and other information.
> > > So, if I understand correctly, hooking up sm501-gpio would require
> > > adding functionality the driver to get the GPIO information from the
> > > device tree in preference to the platform_data, if available, and fall
> > > back to the platform_data for existing users?
> > > 
> > > What should the necessary device tree properties look like to replace
> > > sm501_initdata?
> > > 
> > > - Josh Triplett
> > 
> > You need to look at Documentation/devicetree/bindings/gpio/gpio.txt.
> > 
> > Also, you need to add bits to the sm501-gpio driver to register a
> > dynamically allocated range of gpio pins and to populate the
> > gpiochip->of_node pointer.  If that points at a device tree node, then
> > the core code will take care of setting up translation for you.
> 
> What would the resulting device tree look like, given that the sm501
> driver handles several different types of devices?  sm501 doesn't have a
> separate gpio driver; it just has a flag to enable GPIO.  The GPIO
> controller also doesn't have independent resources; as far as I can
> tell, the sm501 knows everything it needs to know in order to drive the
> gpio, except the boolean presence or absence of gpio.
> 
> Currently, to get the sm501 hooked up at all, I wrote this:
> 
> display@1,0 {
>     compatible = "smi,sm501";
>     reg = <1 0x00000000 0x00800000
>            1 0x03e00000 0x00200000>;
>     interrupts = <1 1 3>;
> };
> 
> To hook up the gpio, would I nest an entire gpio@... { ...;
> gpio-controller; } stanza inside that or next to that, or just add the
> gpio-controller; and #gpio-cells lines inside the existing stanza for
> the sm501?

Just add gpio-controller and #gpio-cells.

> 
> Does the gpio@ bit have any semantic significance, or just the
> gpio-controller line and the compatible line?

Nope, that's just the name and address of the device.  It doesn't
affect the gpio binding (although 'pure' gpio controllers should use
the name 'gpio' as a recommended practice).

g.

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