linux-kernel - Re: [PATCH v2 2/3] dmaengine: imx-sdma: add memcpy interface

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Date:   Fri, 13 Jul 2018 08:16:04 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Robin Gong <yibin.gong@....com>
Cc:     vkoul@...nel.org, dan.j.williams@...el.com, shawnguo@...nel.org,
        fabio.estevam@....com, linux@...linux.org.uk,
        linux-arm-kernel@...ts.infradead.org, kernel@...gutronix.de,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
Subject: Re: [PATCH v2 2/3] dmaengine: imx-sdma: add memcpy interface

On Fri, Jul 13, 2018 at 09:08:46PM +0800, Robin Gong wrote:
> Add MEMCPY capability for imx-sdma driver.
> 
> Signed-off-by: Robin Gong <yibin.gong@....com>
> ---
>  drivers/dma/imx-sdma.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 92 insertions(+), 3 deletions(-)
> 
> @@ -1318,6 +1347,63 @@ static struct sdma_desc *sdma_transfer_init(struct sdma_channel *sdmac,
>  	return NULL;
>  }
>  
> +static struct dma_async_tx_descriptor *sdma_prep_memcpy(
> +		struct dma_chan *chan, dma_addr_t dma_dst,
> +		dma_addr_t dma_src, size_t len, unsigned long flags)
> +{
> +	struct sdma_channel *sdmac = to_sdma_chan(chan);
> +	struct sdma_engine *sdma = sdmac->sdma;
> +	int channel = sdmac->channel;
> +	size_t count;
> +	int i = 0, param;
> +	struct sdma_buffer_descriptor *bd;
> +	struct sdma_desc *desc;
> +
> +	if (!chan || !len)
> +		return NULL;
> +
> +	dev_dbg(sdma->dev, "memcpy: %pad->%pad, len=%zu, channel=%d.\n",
> +		&dma_src, &dma_dst, len, channel);
> +
> +	desc = sdma_transfer_init(sdmac, DMA_MEM_TO_MEM,
> +					len / SDMA_BD_MAX_CNT + 1);
> +	if (!desc)
> +		return NULL;
> +
> +	do {
> +		count = min_t(size_t, len, SDMA_BD_MAX_CNT);
> +		bd = &desc->bd[i];
> +		bd->buffer_addr = dma_src;
> +		bd->ext_buffer_addr = dma_dst;
> +		bd->mode.count = count;
> +		desc->chn_count += count;
> +		/* align with sdma->dma_device.copy_align: 4bytes */
> +		bd->mode.command = 0;
> +
> +		dma_src += count;
> +		dma_dst += count;
> +		len -= count;
> +		i++;

NACK.

Please actually look at your code and find out where you do unaligned DMA
accesses. Hint: What happens when this loop body is executed more than once?

Sascha

> +
> +		param = BD_DONE | BD_EXTD | BD_CONT;
> +		/* last bd */
> +		if (!len) {
> +			param |= BD_INTR;
> +			param |= BD_LAST;
> +			param &= ~BD_CONT;
> +		}
> +
> +		dev_dbg(sdma->dev, "entry %d: count: %zd dma: 0x%x %s%s\n",
> +				i, count, bd->buffer_addr,
> +				param & BD_WRAP ? "wrap" : "",
> +				param & BD_INTR ? " intr" : "");
> +
> +		bd->mode.status = param;
> +	} while (len);
> +

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