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:
+#ifndef __DMA_STM32_DMAMUX_H
+#define __DMA_STM32_DMAMUX_H
+#if defined(CONFIG_STM32_DMAMUX)
+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
need too?

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...

- Péter