On Thu, 18 Apr 2013, Arnd Bergmann wrote:
> On Thursday 18 April 2013, Lee Jones wrote:
> > Using the new DMA DT bindings and API, we can register the DMA40 driver
> > as Device Tree capable. Now, when a client attempts to allocate a
> > channel using the DMA DT bindings via its own node, we are able to parse
> > the request and allocate a channel in the correct manor.
>
> s/manor/manner/ ?
>
> > +Optional properties:
> > +- interrupt-parent: Should be the phandle for the interrupt controller
> > + that services interrupts for this device
>
> I would not bother listing the interrupt-parent.
>
> > +Clients
> > +Required properties:
> > +- dmas: Comma seperated list of dma channel requests
> > +- dma-names: Names of the aforementioned requested channels
> > +
> > +Each dmas request consists of 4 cells:
> > + 1. A phandle pointing to the DMA controller
> > + 2. The DMA request line number (only when 'use fixed channel' is set)
> > + 3. Device Type
> > + 4. A 32bit mask specifying; mode, direction and endianess [NB: This list
> > will grow]
> > + bits 1-2: Mode:
> > + 00: Logical
> > + 01: Physical
> > + 10: Operation
> > + 11: Undefined - will most likely return an error
>
> The statement "will most likely return an error" is not very
> specification-like. ;-) Maybe better call it "reserved".
Actually, I wrote this before I wrote the code.
It definitely does return an error. :)
I'll fixup as you requested anyway.
> What is actually an "Operation" channel? Do we need it for slaves?
No idea. It was in the header file, so I thought I'd better reserve a
bit for it early in case it comes in handy later.
> > + bits 3-4: Direction:
> > + 00: Mem to Mem
> > + 01: Mem to Dev
> > + 10: Dev to Mem
> > + 11: Dev to Dev
>
> For slave channels, we only need mem-to-dev and dev-to-mem, so I would
> use only one bit here.
Okay.
> > + bit 5: Endianess:
> > + 0: Little endian
> > + 1: Big endian
> > + bit 6: Use fixed channel:
> > + 0: Use automatic channel selection
> > + 1: Use DMA request line number
>
> I think you have mixed up the "device type" and "request line number".
>
> The request line is what identifies the slave device (which you call
> the device type)
You're right, I am a little confused by them.
I call them 'device type' because that's what they're called already.
Grep for 'dma_dev_type'. This is the number which gets split into
event group and line, like this:
event_group = D40_TYPE_TO_GROUP(dev_type);
event_line = D40_TYPE_TO_EVENT(dev_type);
> and I would put that number first.
So you want me to switch that round so it looks like:
dmas = <<phandle> <dev_type> <fixed_chan> <flags>;
Instead of what I have at the moment:
dmas = <<phandle> <fixed_chan> <dev_type> <flags>;
Correct?
--
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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