Messages in this thread | | | Date | Wed, 11 Jul 2018 09:01:07 +0200 | From | Sascha Hauer <> | Subject | Re: [PATCH v1 1/4] dmaengine: imx-sdma: add memcpy interface |
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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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