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SubjectRe: [PATCH v1 1/4] dmaengine: imx-sdma: add memcpy interface
On Wed, Jul 11, 2018 at 06:56:18AM +0000, Robin Gong wrote:
>
> > -----Original Message-----
> > From: Sascha Hauer [mailto:s.hauer@pengutronix.de]
> > Sent: 2018年7月11日 14:25
> > To: Robin Gong <yibin.gong@nxp.com>
> > Cc: vkoul@kernel.org; dan.j.williams@intel.com; shawnguo@kernel.org; Fabio
> > Estevam <fabio.estevam@nxp.com>; linux@armlinux.org.uk;
> > linux-arm-kernel@lists.infradead.org; kernel@pengutronix.de;
> > dmaengine@vger.kernel.org; linux-kernel@vger.kernel.org; dl-linux-imx
> > <linux-imx@nxp.com>
> > Subject: Re: [PATCH v1 1/4] dmaengine: imx-sdma: add memcpy interface
> >
> > On Wed, Jul 11, 2018 at 12:23:10AM +0800, Robin Gong wrote:
> > > Add MEMCPY support, meanwhile, add SDMA_BD_MAX_CNT instead of
> > > '0xffff'.
> > >
> > > Signed-off-by: Robin Gong <yibin.gong@nxp.com>
> > > ---
> > > +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)
> > > + goto err_out;
> > > +
> > > + do {
> > > + count = min_t(size_t, len, SDMA_BD_MAX_CNT);
> >
> > When len is bigger than 0xffff you initialize count to 0xffff...
> In this case, the data will be split into several bds, for example,
> If the total count is 0x10000, two bd used then. One is for 0xffff,
> Another is for the last 1

And you are doing byte size DMA? Wouldn't word size accesses be more
optimal?

Sascha


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