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

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Date:	Tue, 16 Jun 2009 06:46:47 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Wolfram Sang <w.sang@...gutronix.de>
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

On Tue, Jun 16, 2009 at 3:04 AM, Wolfram Sang<w.sang@...gutronix.de> wrote:
>
>> > 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.

Trouble is a value that suits all needs today probably won't a year
from now.  :-)

>> 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?

Yeah, that sounds appropriate.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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