linux-kernel - Re: [PATCH 2/3] dma: edma: Add support for Cyclic DMA

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Date:	Mon, 21 Oct 2013 12:23:19 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Joel Fernandes <joelf@...com>
Cc:	Matt Porter <matt@...orter.com>, Mark Brown <broonie@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Dan Williams <djbw@...com>, Jyri Sarha <jsarha@...com>,
	Lars Peter-Clausen <lars@...afoo.de>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	alsa-devel@...a-project.org
Subject: Re: [PATCH 2/3] dma: edma: Add support for Cyclic DMA

On Mon, Sep 23, 2013 at 06:05:14PM -0500, Joel Fernandes wrote:
 
> @@ -449,6 +455,138 @@ static struct dma_async_tx_descriptor *edma_prep_slave_sg(
>  	return vchan_tx_prep(&echan->vchan, &edesc->vdesc, tx_flags);
>  }
>  
> +static struct dma_async_tx_descriptor *edma_prep_dma_cyclic(
> +	struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
> +	size_t period_len, enum dma_transfer_direction direction,
> +	unsigned long tx_flags, void *context)
> +{
> +	struct edma_chan *echan = to_edma_chan(chan);
> +	struct device *dev = chan->device->dev;
> +	struct edma_desc *edesc;
> +	dma_addr_t src_addr, dst_addr;
> +	enum dma_slave_buswidth dev_width;
> +	u32 burst;
> +	int i, ret, nr_periods;
> +
> +	if (unlikely(!echan || !buf_len || !period_len))
> +		return NULL;
> +
> +	if (direction == DMA_DEV_TO_MEM) {
> +		src_addr = echan->cfg.src_addr;
> +		dst_addr = buf_addr;
> +		dev_width = echan->cfg.src_addr_width;
> +		burst = echan->cfg.src_maxburst;
> +	} else if (direction == DMA_MEM_TO_DEV) {
> +		src_addr = buf_addr;
> +		dst_addr = echan->cfg.dst_addr;
> +		dev_width = echan->cfg.dst_addr_width;
> +		burst = echan->cfg.dst_maxburst;
> +	} else {
> +		dev_err(dev, "%s: bad direction?\n", __func__);
> +		return NULL;
> +	}
> +
> +	if (dev_width == DMA_SLAVE_BUSWIDTH_UNDEFINED) {
> +		dev_err(dev, "Undefined slave buswidth\n");
> +		return NULL;
> +	}
> +
> +	if (unlikely(buf_len % period_len)) {
> +		dev_err(dev, "Period should be multiple of Buffer length\n");
> +		return NULL;
> +	}
> +
> +	nr_periods = (buf_len / period_len) + 1;
?

consider the case of buf = period_len, above makes nr_period = 2.

Or buf len 100, period len 50, makes nr_period = 3

Both doesnt seem right to me?

--
~Vinod
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