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 17:53:06 +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

HI Peter,

On 09-11-20, 14:09, Peter Ujfalusi wrote:
> 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()

That is correct, so you need this info in allocate somehow..


> 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.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

-- 
~Vinod