linux-kernel - RE: [PATCH v1 1/4] dmaengine: imx-sdma: add memcpy interface

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Message-ID: <DB6PR04MB32238D762101425CC0CEE0F2895A0@DB6PR04MB3223.eurprd04.prod.outlook.com>
Date:   Wed, 11 Jul 2018 07:05:23 +0000
From:   Robin Gong <yibin.gong@....com>
To:     Sascha Hauer <s.hauer@...gutronix.de>
CC:     "vkoul@...nel.org" <vkoul@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH v1 1/4] dmaengine: imx-sdma: add memcpy interface



> -----Original Message-----
> From: Sascha Hauer [mailto:s.hauer@...gutronix.de]
> Sent: 2018年7月11日 15:01
> To: Robin Gong <yibin.gong@....com>
> Cc: vkoul@...nel.org; dan.j.williams@...el.com; shawnguo@...nel.org; Fabio
> Estevam <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; dl-linux-imx
> <linux-imx@....com>
> Subject: Re: [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@...gutronix.de]
> > > Sent: 2018年7月11日 14:25
> > > To: Robin Gong <yibin.gong@....com>
> > > Cc: vkoul@...nel.org; dan.j.williams@...el.com; shawnguo@...nel.org;
> > > Fabio Estevam <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;
> > > dl-linux-imx <linux-imx@....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@....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
Default is words, and I'll force the buswidth to word and set into BD.
sdma->dma_device.copy_align = DMAENGINE_ALIGN_4_BYTES;
> 
> 
> --
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