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

Jassi Brar jaswinder.singh at linaro.org
Wed May 16 08:37:34 EDT 2012

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.

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