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

[Jassi Brar]

On 12 May 2012 05:21, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 05/11/2012 03:06 PM, Jassi Brar wrote:
>> On 12 May 2012 00:58, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>> On 05/10/2012 01:59 PM, Jassi Brar wrote:
> ...
>>>>> client0: i2s {
>>>>>   /* has 2 DMA request output signals: 0, 1 */
>>>>> };
>>>>>
>>>>> client1: spdif {
>>>>>   /* has 2 DMA request signals: 0, 1 */
>>>>> };
>>>>>
>>>> Do we also need to somehow tag these signals for the client to
>>>> differentiate between TX and RX channel ?
>>>
>>> Yes, the client's DT binding would certainly need to describe how many
>>> DMA request signals its HW generates, and give a unique ID to each. The
>>> driver would need to request a DMA channel for a specific one of its DMA
>>> requests.
>>>
>> Did I read "give a unique ID to each" correctly ?
>
> It'd be unique relative to that individual device or DT node, not at any
> larger scope.
>
OK.

>> Could you please take some time out to jot down an example of how a
>> typical client's dma specifier should look.
>
> With this proposal, I'm not sure that the client DT node would need any
> DMA information at all, at least nothing that identifies which DMA
> controllers, channels, or requests are required to service this
> node/device's DMA requests - that routing information is all represented
> in the DMA controller itself.
>
> (I think Arnd made the following point earlier in this thread):
>
> If you did need to put any other information in DT, then that probably
> would go in the DMA client node, since it'd presumably be the same
> irrespective of which DMA controller got used. However, that information
> presumably wouldn't be needed in DT at all, since the driver would know
> it, since it'd be a facet of the HW.
>
> Note: I'm thinking things like DMA physical address (presumably an
> offset from the reg property), DMA access size (presumably a fixed
> property of the HW), DMA burst size (presumably a property of the HW,
> although at least some HW can be programmed to raise the DMA request
> signal with a varying number of FIFO entries free, so not fixed), etc.
>
Yeah, neither did I think a client node should tell more than IDs of
its channels
- which we now decide to simply mention in its binding.

How do I know if you or someone is interested in reworking the patchset
or want me to give it a try?

Thanks,
Jassi