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

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Message-ID: <20201009103019.GD2968@vkoul-mobl>
Date:   Fri, 9 Oct 2020 16:00:19 +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

Hi Peter,

On 09-10-20, 12:04, Peter Ujfalusi wrote:
> On 08/10/2020 15.31, Vinod Koul wrote:
> > Some complex dmaengine controllers have capability to program the
> > peripheral device, so pass on the peripheral configuration as part of
> > dma_slave_config
> >
> > Signed-off-by: Vinod Koul <vkoul@...nel.org>
> > ---
> >  include/linux/dmaengine.h | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index 6fbd5c99e30c..a15dc2960f6d 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -418,6 +418,9 @@ enum dma_slave_buswidth {
> >   * @slave_id: Slave requester id. Only valid for slave channels. The dma
> >   * slave peripheral will have unique id as dma requester which need to be
> >   * pass as slave config.
> > + * @peripheral_config: peripheral configuration for programming peripheral
> > + * for dmaengine transfer
> > + * @peripheral_size: peripheral configuration buffer size
> >   *
> >   * This struct is passed in as configuration data to a DMA engine
> >   * in order to set up a certain channel for DMA transport at runtime.
> > @@ -443,6 +446,8 @@ struct dma_slave_config {
> >  	u32 dst_port_window_size;
> >  	bool device_fc;
> >  	unsigned int slave_id;
> > +	void *peripheral_config;
> > +	size_t peripheral_size;
> 
> Do you foresee a need of src/dst pair of these?
> If we do DEV_TO_DEV with different type of peripherals it is going to
> cause issues.

Not really as the channel already has direction and this is per channel.
If for any any reason subsequent txn is for different direction, I would
expect that parameters are set again before prep_ calls

-- 
~Vinod