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

Sascha Hauer
2018-07-11T07:08:56Z

On Wed, Jul 11, 2018 at 07:05:23AM +0000, Robin Gong wrote:
>
>
> > -----Original Message-----
> > From: Sascha Hauer [mailto:s.hauer at pengutronix.de]
> > Sent: 2018?7?11? 15:01
> > To: Robin Gong <yibin.gong@nxp.com>
> > Cc: vkoul at kernel.org; dan.j.williams at intel.com; shawnguo at kernel.org; Fabio
> > Estevam <fabio.estevam@nxp.com>; linux at armlinux.org.uk;
> > linux-arm-kernel at lists.infradead.org; kernel at pengutronix.de;
> > dmaengine at vger.kernel.org; linux-kernel at 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 06:56:18AM +0000, Robin Gong wrote:
> > >
> > > > -----Original Message-----
> > > > From: Sascha Hauer [mailto:s.hauer at pengutronix.de]
> > > > Sent: 2018?7?11? 14:25
> > > > To: Robin Gong <yibin.gong@nxp.com>
> > > > Cc: vkoul at kernel.org; dan.j.williams at intel.com; shawnguo at kernel.org;
> > > > Fabio Estevam <fabio.estevam@nxp.com>; linux at armlinux.org.uk;
> > > > linux-arm-kernel at lists.infradead.org; kernel at pengutronix.de;
> > > > dmaengine at vger.kernel.org; linux-kernel at 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
> Default is words, and I'll force the buswidth to word and set into BD.
> sdma->dma_device.copy_align = DMAENGINE_ALIGN_4_BYTES;

So guess which alignment the second transfer has when the first has the
size 0xffff.

Sascha

--
Pengutronix e.K. | |
Industrial Linux Solutions | http://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |