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Date: Wed, 5 Jun 2024 14:13:26 -0400
From: Frank Li <Frank.li@nxp.com>
To: Dave Stevenson <dave.stevenson@raspberrypi.com>
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Subject: Re: [PATCH 09/18] dmaengine: bcm2835: Add function to handle DMA
 mapping
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References: <20240524182702.1317935-1-dave.stevenson@raspberrypi.com>
 <20240524182702.1317935-10-dave.stevenson@raspberrypi.com>
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On Fri, May 24, 2024 at 07:26:53PM +0100, Dave Stevenson wrote:
> The code handling DMA mapping is currently incorrect and
> needs a sequence of fixups.

Can you descript what incorrect here? 

> Move the mapping out into a separate function and structure
> to allow for those fixes to be applied more cleanly.
> 
> Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> ---
>  drivers/dma/bcm2835-dma.c | 46 ++++++++++++++++++++++++++++++++-------
>  1 file changed, 38 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
> index aefaa1f01d7f..ef1d95bae84e 100644
> --- a/drivers/dma/bcm2835-dma.c
> +++ b/drivers/dma/bcm2835-dma.c
> @@ -65,6 +65,10 @@ struct bcm2835_cb_entry {
>  	dma_addr_t paddr;
>  };
>  
> +struct bcm2835_dma_chan_map {
> +	dma_addr_t addr;
> +};
> +
>  struct bcm2835_chan {
>  	struct virt_dma_chan vc;
>  
> @@ -74,6 +78,7 @@ struct bcm2835_chan {
>  	int ch;
>  	struct bcm2835_desc *desc;
>  	struct dma_pool *cb_pool;
> +	struct bcm2835_dma_chan_map map;

I suppose map should in bcm2835_desc.  if put in chan, how about client
driver create two desc by bcm2835_dma_prep_slave_sg()?

prep_slave_sg()
submit()
prep_savle_sg()
submit()
issue_pending()

Frank

>  
>  	void __iomem *chan_base;
>  	int irq_number;
> @@ -268,6 +273,19 @@ static inline bool need_dst_incr(enum dma_transfer_direction direction)
>  	}
>  
>  	return false;
> +};
> +
> +static int bcm2835_dma_map_slave_addr(struct dma_chan *chan,
> +				      phys_addr_t dev_addr,
> +				      size_t dev_size,
> +				      enum dma_data_direction dev_dir)
> +{
> +	struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
> +	struct bcm2835_dma_chan_map *map = &c->map;
> +
> +	map->addr = dev_addr;
> +
> +	return 0;
>  }
>  
>  static void bcm2835_dma_free_cb_chain(struct bcm2835_desc *desc)
> @@ -734,13 +752,19 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_slave_sg(
>  	}
>  
>  	if (direction == DMA_DEV_TO_MEM) {
> -		if (c->cfg.src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
> +		if (bcm2835_dma_map_slave_addr(chan, c->cfg.src_addr,
> +					       c->cfg.src_addr_width,
> +					       DMA_TO_DEVICE))
>  			return NULL;
> -		src = c->cfg.src_addr;
> +
> +		src = c->map.addr;
>  	} else {
> -		if (c->cfg.dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
> +		if (bcm2835_dma_map_slave_addr(chan, c->cfg.dst_addr,
> +					       c->cfg.dst_addr_width,
> +					       DMA_FROM_DEVICE))
>  			return NULL;
> -		dst = c->cfg.dst_addr;
> +
> +		dst = c->map.addr;
>  	}
>  
>  	/* count frames in sg list */
> @@ -795,14 +819,20 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
>  			      __func__, buf_len, period_len);
>  
>  	if (direction == DMA_DEV_TO_MEM) {
> -		if (c->cfg.src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
> +		if (bcm2835_dma_map_slave_addr(chan, c->cfg.src_addr,
> +					       c->cfg.src_addr_width,
> +					       DMA_TO_DEVICE))
>  			return NULL;
> -		src = c->cfg.src_addr;
> +
> +		src = c->map.addr;
>  		dst = buf_addr;
>  	} else {
> -		if (c->cfg.dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
> +		if (bcm2835_dma_map_slave_addr(chan, c->cfg.dst_addr,
> +					       c->cfg.dst_addr_width,
> +					       DMA_FROM_DEVICE))
>  			return NULL;
> -		dst = c->cfg.dst_addr;
> +
> +		dst = c->map.addr;
>  		src = buf_addr;
>  	}
>  
> -- 
> 2.34.1
>