linux-kernel - Re: [PATCH v2] dmaengine: add CSR SiRFprimaII DMAC driver

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Date:	Sat, 17 Sep 2011 00:25:56 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Barry Song <Baohua.Song@....com>
Cc:	vinod.koul@...el.com, Arnd Bergmann <arnd@...db.de>,
	Jassi Brar <jaswinder.singh@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org, workgroup.linux@....com,
	Rongjun Ying <rongjun.ying@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] dmaengine: add CSR SiRFprimaII DMAC driver

On Fri, Sep 16, 2011 at 3:26 PM, Barry Song <Baohua.Song@....com> wrote:

> +static int sirfsoc_dma_slave_config(struct sirfsoc_dma_chan *schan,
> +       struct dma_slave_config *config)
> +{
> +       u32 addr, direction;
> +       unsigned long flags;
> +
> +       switch (config->direction) {
> +       case DMA_FROM_DEVICE:
> +               direction = 0;
> +               addr = config->dst_addr;
> +               break;
> +
> +       case DMA_TO_DEVICE:
> +               direction = 1;
> +               addr = config->src_addr;
> +               break;
> +
> +       default:
> +               return -EINVAL;
> +       }
> +
> +       if ((config->src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES) ||
> +               (config->dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES))
> +               return -EINVAL;
> +
> +       spin_lock_irqsave(&schan->lock, flags);
> +       schan->addr = addr;
> +       schan->direction = direction;
> +       schan->mode = (config->src_maxburst == 4 ? 1 : 0);
> +       spin_unlock_irqrestore(&schan->lock, flags);
> +
> +       return 0;
> +}
You don't need to pass as much info via dma_slave_config as you do here.

dmaxfer_template.src_inc  && !dmaxfer_template.dst_inc  => DMA_TO_DEVICE
!dmaxfer_template.src_inc  && dmaxfer_template.dst_inc  => DMA_FROM_DEVICE

Pass addresses using dmaxfer_template.src_start and dmaxfer_template.dst_start
instead of dma_slave_config.dst_addr and dma_slave_config.src_addr

So, currently you need dma_slave_config only to pass src_addr_width,
dst_addr_width and src_maxburst to the dmac driver.


> +
> +static struct dma_async_tx_descriptor *sirfsoc_dma_prep_slave_sg(
> +       struct dma_chan *chan, struct scatterlist *sgl,
> +       unsigned int sg_len, enum dma_data_direction direction,
> +       unsigned long flags)
> +{
> +       return NULL;
> +}
> +
In v3 I'll remove the BUG_ON check that requires every SLAVE channel
provides device_prep_slave_sg, so you should be able to simply discard
this stub.
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