Re: [PATCH v3 2/6] dmaengine: Add interleaved cyclic transaction type

From: Vinod Koul <vkoul@kernel.org>
To: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	dmaengine@vger.kernel.org, Michal Simek <michal.simek@xilinx.com>,
	Hyun Kwon <hyun.kwon@xilinx.com>,
	Tejas Upadhyay <tejasu@xilinx.com>,
	Satish Kumar Nagireddy <SATISHNA@xilinx.com>
Subject: Re: [PATCH v3 2/6] dmaengine: Add interleaved cyclic transaction type
Date: Thu, 23 Jan 2020 14:13:52 +0530	[thread overview]
Message-ID: <20200123084352.GU2841@vkoul-mobl> (raw)
In-Reply-To: <2f3a9e9e-9b74-7c2e-de3a-4897ab0e8205@ti.com>

On 23-01-20, 10:03, Peter Ujfalusi wrote:
> Hi Laurent,
> 
> On 23/01/2020 4.29, Laurent Pinchart wrote:
> > The new interleaved cyclic transaction type combines interleaved and
> > cycle transactions. It is designed for DMA engines that back display
> > controllers, where the same 2D frame needs to be output to the display
> > until a new frame is available.
> > 
> > Suggested-by: Vinod Koul <vkoul@kernel.org>
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > ---
> >  drivers/dma/dmaengine.c   |  8 +++++++-
> >  include/linux/dmaengine.h | 18 ++++++++++++++++++
> >  2 files changed, 25 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > index 03ac4b96117c..4ffb98a47f31 100644
> > --- a/drivers/dma/dmaengine.c
> > +++ b/drivers/dma/dmaengine.c
> > @@ -981,7 +981,13 @@ int dma_async_device_register(struct dma_device *device)
> >  			"DMA_INTERLEAVE");
> >  		return -EIO;
> >  	}
> > -
> > +	if (dma_has_cap(DMA_INTERLEAVE_CYCLIC, device->cap_mask) &&
> > +	    !device->device_prep_interleaved_cyclic) {
> > +		dev_err(device->dev,
> > +			"Device claims capability %s, but op is not defined\n",
> > +			"DMA_INTERLEAVE_CYCLIC");
> > +		return -EIO;
> > +	}
> >  
> >  	if (!device->device_tx_status) {
> >  		dev_err(device->dev, "Device tx_status is not defined\n");
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index 8fcdee1c0cf9..e9af3bf835cb 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -61,6 +61,7 @@ enum dma_transaction_type {
> >  	DMA_SLAVE,
> >  	DMA_CYCLIC,
> >  	DMA_INTERLEAVE,
> > +	DMA_INTERLEAVE_CYCLIC,
> >  /* last transaction type for creation of the capabilities mask */
> >  	DMA_TX_TYPE_END,
> >  };
> > @@ -701,6 +702,10 @@ struct dma_filter {
> >   *	The function takes a buffer of size buf_len. The callback function will
> >   *	be called after period_len bytes have been transferred.
> >   * @device_prep_interleaved_dma: Transfer expression in a generic way.
> > + * @device_prep_interleaved_cyclic: prepares an interleaved cyclic transfer.
> > + *	This is similar to @device_prep_interleaved_dma, but the transfer is
> > + *	repeated until a new transfer is issued. This transfer type is meant
> > + *	for display.
> 
> I think capture (camera) is another potential beneficiary of this.
> 
> So you don't need to terminate the running interleaved_cyclic and start
> a new one, but prepare and issue a new one, which would
> terminate/replace the currently running cyclic interleaved DMA?

Why not explicitly terminate the transfer and start when a new one is
issued. That can be common usage for audio and display..

-- 
~Vinod