linux-kernel - Re: [PATCH 2/2] uio: add an of

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Message-ID: <20090616090435.GA21321@pengutronix.de>
Date:	Tue, 16 Jun 2009 11:04:35 +0200
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org, devicetree-discuss@...abs.org,
	"Hans J. Koch" <hjk@...utronix.de>,
	Magnus Damm <magnus.damm@...il.com>, linuxppc-dev@...abs.org,
	Greg KH <gregkh@...e.de>
Subject: Re: [PATCH 2/2] uio: add an of_genirq driver


> > diff --git a/Documentation/powerpc/dts-bindings/uio-generic.txt b/Documentation/powerpc/dts-bindings/uio-generic.txt
> > new file mode 100644
> > index 0000000..8ad9861
> > --- /dev/null
> > +++ b/Documentation/powerpc/dts-bindings/uio-generic.txt
> > @@ -0,0 +1,16 @@
> > +UIO for custom devices
> > +
> > +A device which will be mapped using the UIO subsystem.
> > +
> > +Properties:
> > + - compatible : should contain the specific model used, followed by
> > +                "generic-uio".
> > + - reg : address range(s) of the device (up to MAX_UIO_MAPS)
> > + - interrupts : interrupt of the device
> > +
> > +Example:
> > +        c64fpga@0 {
> > +                compatible = "ptx,c64fpga001", "generic-uio";
> > +                reg = <0x0 0x10000>;
> > +                interrupts = <0 0 3>;
> > +        };
> 
> Hmmm, I'm not happy about this.  The device tree describes the
> hardware, not the way Linux uses the hardware.  UIO definitely falls
> into the category of Linux implementation detail.

Yes, I am aware of that. I just started with the mechanisms which are available
today and hoped we could find some compatible-value which will suit all needs.

> This should be approached from the other way around.  Either the
> generic-uio of_platform driver should contain an explicit list of
> devices to be handled by UIO,

Well, that could lead to a quite huge match_table over time.

> or the OF infrastructure should be modified to allow things like force
> binding of_devices to of_drivers at runtime.

That is an interesting idea. I could imagine something like a 'new_compatible"
entry in the sysfs-section of the driver similar to 'new_id' for PCI. After
writing a new compatible-string into it, matching will triggered again with the
new entry added. That could (should?) also be placed at the of-core-level. Or
did you have something else in mind?

Regards,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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