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 17:15:34 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
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


Hey Peter,

On 28-10-20, 11:56, Peter Ujfalusi wrote:
> 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.

We get 'channel' in xlate, so wont that help? I think I am still missing
something here :(


-- 
~Vinod