linux-kernel - Re: [PATCH v4 6/8] dmaengine: rcar-dmac: add iommu support for slave transfers

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Date:	Mon, 7 Mar 2016 11:33:49 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Niklas Söderlund 
	<niklas.soderlund+renesas@...natech.se>
Cc:	linux-renesas-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org, iommu@...ts.linux-foundation.org,
	robin.murphy@....com, laurent.pinchart@...asonboard.com,
	geert+renesas@...der.be, linus.walleij@...aro.org,
	dan.j.williams@...el.com, arnd@...db.de, linux-arch@...r.kernel.org
Subject: Re: [PATCH v4 6/8] dmaengine: rcar-dmac: add iommu support for slave
 transfers

On Tue, Feb 16, 2016 at 09:39:42PM +0100, Niklas Söderlund wrote:
> Enable slave transfers to devices behind IPMMU:s by mapping the slave

IPMMU:s ?

> addresses using the dma-mapping API.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> ---
>  drivers/dma/sh/rcar-dmac.c | 52 +++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 47 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
> index 743873c..6a24847 100644
> --- a/drivers/dma/sh/rcar-dmac.c
> +++ b/drivers/dma/sh/rcar-dmac.c
> @@ -1106,21 +1106,63 @@ rcar_dmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
>  	return desc;
>  }
>  
> +static int rcar_dmac_set_slave_addr(struct dma_chan *chan,
> +				     struct rcar_dmac_chan_slave *slave,
> +				     phys_addr_t addr, size_t size)
> +{
> +	enum dma_data_direction dir;
> +
> +	/*
> +	 * We can't know the direction at this time, see documentation for
> +	 * 'direction' in struct dma_slave_config.
> +	 */

Okay so we are mapping on the device config, which doesn't seem intutive.
Why is this not done during prepare calls?

> +	dir = DMA_BIDIRECTIONAL;
> +
> +	if (slave->xfer_size) {
> +		dma_unmap_resource(chan->device->dev, slave->slave_addr,
> +				   slave->xfer_size, dir, NULL);
> +		slave->slave_addr = 0;
> +		slave->xfer_size = 0;
> +	}
> +
> +	if (size) {
> +		slave->slave_addr = dma_map_resource(chan->device->dev, addr,
> +				size, dir, NULL);
> +
> +		if (dma_mapping_error(chan->device->dev, slave->slave_addr)) {
> +			struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
> +
> +			dev_err(chan->device->dev,
> +				"chan%u: failed to map %zx@...p", rchan->index,
> +				size, &addr);
> +			return -EIO;
> +		}
> +
> +		slave->xfer_size = size;
> +	}
> +
> +	return 0;
> +}
> +
>  static int rcar_dmac_device_config(struct dma_chan *chan,
>  				   struct dma_slave_config *cfg)
>  {
>  	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
> +	int ret;
>  
>  	/*
>  	 * We could lock this, but you shouldn't be configuring the
>  	 * channel, while using it...
>  	 */
> -	rchan->src.slave_addr = cfg->src_addr;
> -	rchan->dst.slave_addr = cfg->dst_addr;
> -	rchan->src.xfer_size = cfg->src_addr_width;
> -	rchan->dst.xfer_size = cfg->dst_addr_width;
>  
> -	return 0;
> +	ret = rcar_dmac_set_slave_addr(chan, &rchan->src, cfg->src_addr,
> +				       cfg->src_addr_width);
> +	if (ret)
> +		return ret;
> +
> +	ret = rcar_dmac_set_slave_addr(chan, &rchan->dst, cfg->dst_addr,
> +				       cfg->dst_addr_width);
> +	return ret;
>  }
>  
>  static int rcar_dmac_chan_terminate_all(struct dma_chan *chan)
> -- 
> 2.7.1
> 

-- 
~Vinod