RE: Xilinx SYSACE driver and 8-bit attachment

[John Linn]

> -----Original Message-----
> From: John Williams [mailto:john.williams@xxxxxxxxxxxxx]
> Sent: Wednesday, October 07, 2009 5:45 PM
> To: grant.likely@xxxxxxxxxxxx
> Cc: Linux Kernel list; Michal Simek; John Linn; David DeBonis; Stephen Neuendorffer; devicetree-
> discuss
> Subject: Re: Xilinx SYSACE driver and 8-bit attachment
> 
> On Wed, Oct 7, 2009 at 11:34 PM, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote:
> > [Added devicetree-discuss to cc: list]
> >
> > On Wed, Oct 7, 2009 at 1:13 AM, John Williams
> > <john.williams@xxxxxxxxxxxxx> wrote:
> >> Hi Grant (it's your driver :) and David D ( and your DTS generator :)
> > [...]
> >> if (of_find_property(op->node, "8-bit", NULL))
> > [...]
> >> doesn't match the properties generated by Xilinx's device tree generator:
> > [...]
> >>                         xlnx,mem-width = <0x8>;
> >>
> >> So, the question is, which should change?
> >
> > Well, obviously its a device tree generator bug, the driver code is
> > perfect.  :-P
> 
> How did I know you'd say that? :)
> 
> > In all seriousness though, the '8-bit' property has been present for a
> > while now and needs to be retained to not break existing users.  It
> > would be okay for the driver to be modified to *also* check for the
> > xlnx,mem-width property, but the better solution is to modify the
> > device tree generator.  Plus, the '8-bit' property is the documented
> > binding in Documentation/powerpc/dts-bindings/xilinx.txt
> 
> I tend to agree - but I also tend think that putting funky, arbitrary
> output strings in the DTS generator is also a bad idea.
> 
> In this case, my vote is leaning towards adding a test for
> "xlnx,mem-width = <..>" to the driver, in addition to the existing
> "8-bit" tag to keep back compatability.
> 
> How would you feel about that?
> 
> In future, for new Xilinx drivers I think the default binding should
> be inspired by what comes from the DTS generator automatically, with
> out any special per-device hacks.  This has a natural tendency towards
> minimum pain I think.

Agreed. This was special legacy is the only reason it warranted it.

> 
> John
> --
> John Williams, PhD, B.Eng, B.IT
> PetaLogix - Linux Solutions for a Reconfigurable World
> w: www.petalogix.com  p: +61-7-30090663  f: +61-7-30090663


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