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

[Jassi Brar]

Hi Jon,

On 16 May 2012 06:41, Jon Hunter <jon-hunter at ti.com> wrote:
> On 05/04/2012 02:01 PM, Jassi Brar wrote:
>>
>> +       i2c1: i2c at 1 {
>> +               ...
>> +               dma = <&sdma 2 1 &sdma 3 2>;
>> +               ...
>> +       };
>>>
>> I see this requires a client driver to specify a particular req_line on a
>> particular dma controller. I am not sure if this is most optimal.
>
> Actually, no. The phandle in the DT specifies the DMA controller to use.
> Then the client simply asks for a channel with a particular property,
> for example, DMA_MEM_TO_DEV (ie. TX) and the channel information is return.
>
See below.

>> I think such client->req_line map should be provided to the dmac controller
>> driver via its dt node in some format. The dmac driver could then populate
>> a dma_chan, or similar, only for that req_line and not for the unused one
>> which otherwise could also have served the same client.
>>
>> Ideally the I2C driver should simply ask, say, a channel for TX and another
>> for RX, everything else should already be setup via dmac's dt nodes.
>
> Yes that is the intention here.
>
But the client is required to specify the dmac that would serve it.
Which is more
than simply asking for "some suitable channel".

If you read the whole exchange between I and Stephen, we converged on a
scheme of clients' node having nothing to specify and DMAC told all about
every client in one palce. Which resembles closer to reality and is
much simpler.
I already started on a patchset and should be able submit for review
in a day or two.