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

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Date:   Fri, 9 Oct 2020 14:29:44 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vinod Koul <vkoul@...nel.org>
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 09/10/2020 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?

>>
>> If only one of them needs config, then sure, the driver can pin-point
>> which one the single config might apply to.
>>
>> Or you chain the same type of peripheral and you would need different
>> config for tx and rx?
>>
>> - Péter
>>
>> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
>> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> 

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki