[PATCH RFC v5 4/5] dma: mpc512x: register for device tree channel lookup
Mark Rutland
mark.rutland at arm.com
Tue Nov 19 02:23:57 EST 2013
On Mon, Nov 18, 2013 at 02:31:54PM +0000, Arnd Bergmann wrote:
> On Monday 18 November 2013, Mark Rutland wrote:
> > > +++ b/Documentation/devicetree/bindings/dma/mpc512x-dma.txt
> > > @@ -0,0 +1,55 @@
> > > +* Freescale MPC512x DMA Controller
> > > +
> > > +The DMA controller in the Freescale MPC512x SoC can move blocks of
> > > +memory contents between memory and peripherals or memory to memory.
> > > +
> > > +Refer to the "Generic DMA Controller and DMA request bindings" description
> > > +in the dma.txt file for a more detailled discussion of the binding. The
> > > +MPC512x DMA engine binding follows the common scheme, but doesn't provide
> > > +support for the optional channels and requests counters (those values are
> > > +derived from the detected hardware features) and has a fixed client
> > > +specifier length of 1 integer cell (the value is the DMA channel, since
> > > +the DMA controller uses a fixed assignment of request lines per channel).
> >
> > The fact that #dma-cells must be <1> isn't a difference from the
> > standard binding, and needs not be described here. The meaning of the
> > value should be in your description of #dma-cells below.
>
> I think the value it has to be in there, and I have in the past asked other
> people to add this. Note that in the generic binding, it says that it must
> be "at least 1". You can have controllers that require a larger number, or
> that can use 1 or 2 alternatively, depending on how the device is wired
> up, e.g. when a dma controller has two master ports you would need a
> second cell to specify the port number, but only if more than one port
> is actually connected to a slave.
The number of cells required should be described. My points were that it
should be described at the property description rather than in the introduction,
and that the fact that a specific value was required was not a
difference from the bindings as the paragraph implied.
>
> > I'm not sure it's worth mentioning optional channels / request counters.
> > If anything, it would be better to update dma.txt to move the "Optional
> > properties" to something like "Suggested properties"...
>
> These are less clearly defined. In the generic binding, it's mostly a matter
> of "if you need to pass this information, use these properties". The individual
> binding can then make them mandatory if needed.
Agreed. I'd prefer that bindings described the suggested properties they
used, rather than those they don't.
Thanks,
Mark.
More information about the Linuxppc-dev
mailing list