[PATCH V2 6/6] spi/spi-pl022: Request/free DMA channels as and when required.

[Jassi Brar]

On Wed, Aug 10, 2011 at 2:59 PM, viresh kumar <viresh.kumar at st.com> wrote:
> On 08/10/2011 02:30 PM, Russell King - ARM Linux wrote:
>>> > They must be allocated when they are required and must be freed after we are
>>> > done with transfers. So that they can be used by other users.
>> Which DMA engine driver requires this?
>>
>
> dw_dmac.c
>
>> Normally, when we have DMA engine drivers with multiple request signals,
>> the slave peripheral side publishes several virtual channels which are
>> claimed by the peripheral drivers.  This (amongst other things) allows
>> the peripheral drivers to hold claim to one of the virtual channels
>> all the time that it's required.
>
> If users of DMA expect DMA engine drivers to work this way, then we should
> have this mentioned clearly in DMA slave documentation.

The requirement stems from the fact that most DMACs(esp third party) could be
made to reroute req-signals by the platform, it has not much to do with the API.
IMO, all dmac drivers should be implemented that way to be on the safer side.