linux-kernel - Re: [PATCH 01/18] dmaengine: of-dma: Add support for optional router configuration callback

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Date:   Mon, 9 Nov 2020 14:09:03 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vinod Koul <vkoul@...nel.org>
CC:     <nm@...com>, <ssantosh@...nel.org>, <robh+dt@...nel.org>,
        <vigneshr@...com>, <dan.j.williams@...el.com>, <t-kristo@...com>,
        <lokeshvutla@...com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <dmaengine@...r.kernel.org>
Subject: Re: [PATCH 01/18] dmaengine: of-dma: Add support for optional router
 configuration callback

Hi Vinod,

On 09/11/2020 13.45, Vinod Koul wrote:
>> Without a channel number I can not do anything.
>> It is close to a chicken and egg problem.
> 
> We get 'channel' in xlate, so wont that help? I think I am still missing
> something here :(

Yes, we get channel in xlate, but we get the channel after
ofdma->of_dma_route_allocate()

of_dma_route_allocate() si the place where DMA routers create the
dmaspec for the DMA controller to get a channel and they up until BCDMA
did also the HW configuration to get the event routed.

For a BCDMA channel we can have three triggers:
Global trigger 0 for the channel
Global trigger 1 for the channel
Local trigger for the channel

Every BCDMA channel have these triggers and for all of them they are the
same (from the channel's pow).
bchan0 can be triggered by global trigger 0
bchan1 can be triggered by global trigger 0

But these triggers are not the same ones, the real trigger depends on
the router, which of it's input is converted to send out an event to
trigger bchan0_trigger0 or to trigger bchan1_trigger0.

When we got the channel with the dmaspec from the router driver then we
need to tell the router driver that it needs to send a given event in
order to trigger the channel that we got.

We can not have traditional binding for BCDMA either where we would tell
the bchan index to be used because depending on the resource allocation
done within sysfw that exact channel might not be even available for us.

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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