Subject: [PATCH V3 1/2] of: Add generic device tree DMA helpers

From: [email-masked] (Jon Hunter)
Date: Wed, 16 May 2012 12:37:54 -0500

On 05/16/2012 12:24 PM, Jassi Brar wrote:
> On 16 May 2012 22:42, Jon Hunter <[email-masked]> wrote:
> 
>>>> 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.

Jon