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

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Message-ID: <cf3d3de0-223b-4846-bd9f-b78654ae2d08@ti.com>
Date:   Wed, 28 Oct 2020 11:56:06 +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 28/10/2020 7.55, Vinod Koul wrote:

>> To summarize:
>> In of_dma_route_allocate() the router does not yet know the channel we
>> are going to get.
>> In of_dma_xlate() the DMA driver does not yet know if the channel will
>> use router or not.
>> I need to tell the router the event number it has to send, which is
>> based on the channel number I got.
> 
> Sounds reasonable, btw why not pass this information in xlate. Router
> will have a different xlate rather than non router right, or is it same.

Yes, the router's have their separate xlate, but in that xlate we do not
yet have a channel. I don't know what is the event I need to send from
the router to trigger the channel.

> If this information is anyway available in DT might be better to get it
> and use from DT

Without a channel number I can not do anything.
It is close to a chicken and egg problem.

- Péter

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