linux-kernel - Re: [PATCH v3 2/3] dmaengine: add peripheral configuration

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Message-ID: <20201007112807.GW2968@vkoul-mobl>
Date:   Wed, 7 Oct 2020 16:58:07 +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 v3 2/3] dmaengine: add peripheral configuration

Hi Peter,

On 02-10-20, 11:48, Peter Ujfalusi wrote:

> It depends which is best for the use case.
> I see the metadata useful when you need to send different
> metadata/configuration with each transfer.
> It can be also useful when you need it seldom, but for your use case and
> setup the dma_slave_config extended with
> 
> enum dmaengine_peripheral peripheral_type;
> void *peripheral_config;
> 
> would be a bit more explicit.
> 
> I would then deal with the peripheral config in this way:
> when the DMA driver's device_config is called, I would take the
> parameters and set a flag that the config needs to be processed as it
> has changed.
> In the next prep_slave_sg() then I would prepare the TREs with the
> config and clear the flag that the next transfer does not need the
> configuration anymore.
> 
> In this way each dmaengine_slave_config() will trigger at the next
> prep_slave_sg time configuration update for the peripheral to be
> included in the TREs.
> The set_config would be internal to the DMA driver, clients just need to
> update the configuration when they need to and everything is taken care of.

Ok I am going to drop the dmaengine_peripheral and make
peripheral_config as as you proposed.

So will add following to dma_slave_config:
        void *peripheral_config;

Driver can define the config they would like and use.

We can eventually look at common implementations and try to unify once
we have more users

-- 
~Vinod