Re: [PATCH v3 2/5] dmaengine: Add STM32 DMAMUX driver
From: Peter Ujfalusi
Date: Wed Aug 02 2017 - 05:19:56 EST
On 2017-08-02 07:55, Vinod Koul wrote:
On Tue, Aug 01, 2017 at 09:32:50AM +0000, Pierre Yves MORDRET wrote:
On 07/31/2017 02:31 PM, Vinod Koul wrote:
On Wed, Jul 26, 2017 at 07:38:02AM +0000, Pierre Yves MORDRET wrote:
+int stm32_dmamux_set_config(struct device *dev, void *route_data, u32 chan_id);
Why do we need a custom API in this case?
This API is called by DMA when a slave is requested by client. DMA can work
without DMAMUX this API has been put in place to configure DMAMUX whether client
is requesting a DMAMUX Channel instead of a DMA one.
You mean the dmaengine driver right?
Yes. The API is mainly called by "device_config" through out STM32 DMA Driver
when a router is in place for client.
Please refer to Patch 4/5 on this set.
Okay am thinking on why this can't be generic..? An optional router config
I would have liked to answer there is a callback within engine but unfortunately
I didn't figure out one when I did my router's development. I've looked once
more but again I can't find how to map chanID and request line without custom API.
Yes there is no callback for routers but we can add a generic callback
here to be used. I added Peter for his comments, isn't that something they
The event router via of_dma_router_register() should be capable of
handling different type of muxers, like the ti-dma-crossbar.c is doing
for two different type of event crossbars.
Basically with the of_dma_route_allocate you craft a dma_spec which can
be understood by the dma-master pointed form the router's node.
You do the configuration of the mux in this function, craft the dma_spec
and that's it. In DT the peripherals are using the router's node for DMA
binding and everything is transparent for them.
Note: The use of am335x xbar in the ti-dma-crossbar is optional and only
needed when we need to have different event than the default for a
specific dma request line.
If you normally use the DMA like this:
dmas = <&edma 129 1>, <&ddma_xbar 128 1>;
dma-names = "tx", "rx";
If you have DMA event router/mux, then depending on how it works you
might have different number of parameters. In my case the DRA7 crossbar
does not need extra parameter, so to get it in use:
dmas = <&edma_xbar 129 1>, <&edma_xbar 128 1>;
dma-names = "tx", "rx";
The router driver will rewrite the dma_spec and replace the 129/128 and
pass something different to the dma-master (dynamic event mapping).
On am335x we have different xbar type so there:
dmas = <&edma_xbar 12 0 1>, <&edma_xbar 13 0 2>;
Out from this the router driver will create a spec equivalent to
dmas = <&edma_xbar 12 0>, <&edma_xbar 13 0>;
But it will change the xbar that DMA request 12/13 will not have the
default event routed to.
I believe that the dma_router infra we have in dmaengine can cover most
if not all use cases...