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

[Robin Gong]

> -----Original Message-----
> From: Sascha Hauer [mailto:s.ha...@pengutronix.de]
> Sent: 2018年7月11日 15:01
> To: Robin Gong <yibin.g...@nxp.com>
> Cc: vk...@kernel.org; dan.j.willi...@intel.com; shawn...@kernel.org; Fabio
> Estevam <fabio.este...@nxp.com>; li...@armlinux.org.uk;
> linux-arm-ker...@lists.infradead.org; ker...@pengutronix.de;
> dmaeng...@vger.kernel.org; linux-kernel@vger.kernel.org; dl-linux-imx
> <linux-...@nxp.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.ha...@pengutronix.de]
> > > Sent: 2018年7月11日 14:25
> > > To: Robin Gong <yibin.g...@nxp.com>
> > > Cc: vk...@kernel.org; dan.j.willi...@intel.com; shawn...@kernel.org;
> > > Fabio Estevam <fabio.este...@nxp.com>; li...@armlinux.org.uk;
> > > linux-arm-ker...@lists.infradead.org; ker...@pengutronix.de;
> > > dmaeng...@vger.kernel.org; linux-kernel@vger.kernel.org;
> > > dl-linux-imx <linux-...@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.g...@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
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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