linux-kernel - Re: [PATCH v4 2/3] dmaengine: add peripheral configuration

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Message-ID: <20201012060916.GI2968@vkoul-mobl>
Date:   Mon, 12 Oct 2020 11:39:16 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     dmaengine@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] dmaengine: add peripheral configuration

On 09-10-20, 14:29, Peter Ujfalusi wrote:
> 
> 
> On 09/10/2020 14.15, Vinod Koul wrote:
> >>> If for any any reason subsequent txn is for different direction, I would
> >>> expect that parameters are set again before prep_ calls
> >>
> >> But in DEV_TO_DEV?
> > 
> > Do we support that :D
> > 
> >> If we have two peripherals, both needs config:
> >> p1_config and p2_config
> >>
> >> What and how would one use the single peripheral_config?
> > 
> > Since the config is implementation specific, I do not think it limits.
> > You may create
> > 
> > struct peter_config {
> >         struct p1_config;
> >         struct p2_config;
> > };
> 
> The use case is:
> MEM -DMA-> P1 -DMA-> P2
> or
> P2 -DMA-> P1 -DMA-> MEM
> or
> MEM -DMA-> P2
> or
> P2 -DMA-> MEM
> or
> MEM -DMA-> P1 -DMA-> MEM
> 
> How would the DMA guess what it should do? How would the independent P1
> and P2 would know how to set up the config?

As I said, we do not support DEV_TO_DEV yet :)

Question is how would p1<-->p2 look, will p1 initiate a DMA txn or p2..?
who will configure these..

Do you have a real world example in horizon...

-- 
~Vinod