RE: [PATCH v1 3/4] dmaengine: imx-sdma: support dmatest

[Robin Gong]

> -----Original Message-----
> From: Vinod [mailto:vkoul@xxxxxxxxxx]
> Sent: 2018å7æ11æ 15:19
> To: s.hauer@xxxxxxxxxxxxxx
> Cc: Robin Gong <yibin.gong@xxxxxxx>; dan.j.williams@xxxxxxxxx;
> shawnguo@xxxxxxxxxx; Fabio Estevam <fabio.estevam@xxxxxxx>;
> linux@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> kernel@xxxxxxxxxxxxxx; dmaengine@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>
> Subject: Re: [PATCH v1 3/4] dmaengine: imx-sdma: support dmatest
> 
> On 11-07-18, 08:53, s.hauer@xxxxxxxxxxxxxx wrote:
> > On Wed, Jul 11, 2018 at 06:37:02AM +0000, Robin Gong wrote:
> > >
> > > > -----Original Message-----
> > > > From: Vinod [mailto:vkoul@xxxxxxxxxx]
> > > > Sent: 2018å7æ10æ 23:33
> > > > To: Robin Gong <yibin.gong@xxxxxxx>
> > > > Cc: dan.j.williams@xxxxxxxxx; shawnguo@xxxxxxxxxx;
> > > > s.hauer@xxxxxxxxxxxxxx; Fabio Estevam <fabio.estevam@xxxxxxx>;
> > > > linux@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > > kernel@xxxxxxxxxxxxxx; dmaengine@xxxxxxxxxxxxxxx;
> > > > linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>
> > > > Subject: Re: [PATCH v1 3/4] dmaengine: imx-sdma: support dmatest
> > > >
> > > > On 11-07-18, 00:23, Robin Gong wrote:
> > > > > dmatest(memcpy) will never call dmaengine_slave_config before
> > > > > prep,
> > > >
> > > > and that should have been a hint to you that you should not expect
> > > > that
> > > >
> > > > > so jobs in dmaengine_slave_config need to be moved into
> > > > > somewhere before device_prep_dma_memcpy. Besides, dmatest never
> > > > > setup chan
> > > > > ->private as other common case like uart/audio/spi will always
> > > > > ->setup
> > > > > chan->private. Here check it to judge if it's dmatest case and
> > > > > chan->do
> > > > > jobs in slave_config.
> > > >
> > > > and you should not do anything for dmatest. Supporting it means
> > > > memcpy implementation is not correct :)
> > > Okay, I will any word about dmatest here since memcpy assume no
> > > calling slave_config.
> > > >
> > > > >
> > > > > Signed-off-by: Robin Gong <yibin.gong@xxxxxxx>
> > > > > ---
> > > > >  drivers/dma/imx-sdma.c | 37
> > > > > ++++++++++++++++++++++++++++---------
> > > > >  1 file changed, 28 insertions(+), 9 deletions(-)
> > > > >
> > > > > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> > > > > index
> > > > > ed2267d..48f3749 100644
> > > > > --- a/drivers/dma/imx-sdma.c
> > > > > +++ b/drivers/dma/imx-sdma.c
> > > > > @@ -1222,10 +1222,36 @@ static int
> > > > > sdma_alloc_chan_resources(struct dma_chan *chan)  {
> > > > >  	struct sdma_channel *sdmac = to_sdma_chan(chan);
> > > > >  	struct imx_dma_data *data = chan->private;
> > > > > +	struct imx_dma_data default_data;
> > > > >  	int prio, ret;
> > > > >
> > > > > -	if (!data)
> > > > > -		return -EINVAL;
> > > > > +	ret = clk_enable(sdmac->sdma->clk_ipg);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +	ret = clk_enable(sdmac->sdma->clk_ahb);
> > > > > +	if (ret)
> > > > > +		goto disable_clk_ipg;
> > > > > +	/*
> > > > > +	 * dmatest(memcpy) will never call dmaengine_slave_config before
> prep,
> > > > > +	 * so jobs in dmaengine_slave_config need to be moved into
> somewhere
> > > > > +	 * before device_prep_dma_memcpy. Besides, dmatest never setup
> chan
> > > > > +	 * ->private as other common cases like uart/audio/spi will setup
> > > > > +	 * chan->private always. Here check it to judge if it's dmatest case
> > > > > +	 * and do jobs in slave_config.
> > > > > +	 */
> > > > > +	if (!data) {
> > > > > +		dev_warn(sdmac->sdma->dev, "dmatest is running?\n");
> > > >
> > > > why is that a warning!
> > > Current SDMA driver assume filter function to set chan->private with
> > > specific data (struct imx_dma_data dma_data)like below
> (sound/soc/fsl/fsl_asrc_dma.c):
> > > static bool filter(struct dma_chan *chan, void *param) {
> > >         if (!imx_dma_is_general_purpose(chan))
> > >                 return false;
> > >         chan->private = param;
> > >         return true;
> > > }
> > >
> > > But in memcpy case, at lease dmatest case, no chan->private set in its filter
> function.
> > > So here take dmatest a special case and do some prepare jobs for
> > > memcpy. But if the Upper device driver call dma_request_channel()
> > > with their specific filter without 'chan->private' setting in the
> > > future. The warning message is a useful hint to them to Add 'chan->private'
> in filter function.  Or doc it somewhere?
> >
> > Instead of doing heuristics to guess whether we are doing memcpy you
> > could instead make memcpy the default when slave_config is not called,
> > i.e. drop the if (!data) check completely.
> >
> > > >
> > > > > +		sdmac->word_size  =
> sdmac->sdma->dma_device.copy_align;
> > > > > +		default_data.priority = 2;
> > > > > +		default_data.peripheral_type = IMX_DMATYPE_MEMORY;
> > > > > +		default_data.dma_request = 0;
> > > > > +		default_data.dma_request2 = 0;
> > > > > +		data = &default_data;
> > > > > +
> > > > > +		sdma_config_ownership(sdmac, false, true, false);
> > > > > +		sdma_get_pc(sdmac, IMX_DMATYPE_MEMORY);
> > > > > +		sdma_load_context(sdmac);
> > > > > +	}
> > > >
> > > > this needs to be default for memcpy
> >
> > The problem seems to be that we do not know whether we are doing
> > memcpy or not. Normally we get the information how a channel is to be
> > configured in dma_device->device_config, but this function is not
> > called in the memcpy case.
> 
> Not really true, device_config only provides parameters to be configured for
> next slave transaction
> 
> > An alternative might also be to do the setup in
> dma_device->device_prep_dma_memcpy.
> 
> Precisely, see how other drivers do this
> 
> Let's roll back a bit and foresee why is this required.
> 
> In case of memcpy, you need to tell DMA to do transfer from src to dstn and
> size. Additional parameters like buswidth etc should be derived for maximum
> throughput (after all we are dma, people want it to be done
> fastest)
> 
> Now for slave, you are interfacing with a peripheral and don't know how that is
> setup. So you need to match the parameters, otherwise you get overflow or
> underflow and hence need for device_config
> 
> Please do not derive additional notions from these, please do not assume
> anything else, unless provided in documentation :)
I will move such prepare jobs from slave_config to device_prep_dma_memcpy
Instead of device_alloc_chan_resources as I did in v1, thus we have no 'chan->private'
issue, just like drivers/dma/stm32-mdma.c. The only limitation is those prepare jobs
(some register setting) will be done every time memcpy instead of only one time in slave_config
or v1 case. Is that ok?
> 
> In doubt, just ask!
> 
> HTH
> --
> ~Vinod