On 05/16/2012 12:46 PM, Stephen Warren wrote:

On 05/16/2012 11:37 AM, Jon Hunter wrote:

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On 05/16/2012 12:24 PM, Jassi Brar wrote:

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On 16 May 2012 22:42, Jon Hunter [off-list ref] wrote:

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What is still unclear to me, is if you use this token approach how
readable is the device-tree? For example, if you have a client that can
use one of two dmac and for each dmac the request/channel number is
different, then by using a global token how can I determine what the
options available for this client are?

Simple - you/client need not know about any option at all :)

Client driver would simply request some channel and if it
doesn't get it, it bails out.

It would be the DMACs' DT node that would contain that info.

Yes, but what if I am doing some custom application and want to modify
the mapping that is being used? So I just wanted to make sure it is easy
to understand assuming that you understand what your h/w is capable of.

Any scenario when a client would want to choose which dma controller
it runs on?

Because when we say a client could be provided a channel on any of the
two given dmacs, it implies that the client wouldn't feel any difference.

That's not my point. I am saying for some reason, maybe QoS, _I_ want to
specify which mapping used. I am the one that knows how the h/w is being
used and _I_ want to customise the dma/channel mapping in the DT, such
that when the client asks for it I know what it is getting. Yes to the
client, it does not care, but I do.

If you really need to do that, you could always just lie in the DT node
of the DMA controllers you don't want to use, and omit the entry for the
DMA client(s) you don't want to use it.

Exactly. The point I am trying to make, is that whatever binding we have
it needs to be intuitive such that someone who knows the hardware could
customise by removing entries, etc. This is probably a mute point now
that we are not using the token scheme, but I wanted to be clear that I
could see people customising the stock dev-trees in the kernel for their
particular application. That's all.

Jon