Re: [PATCH 01/14] dma: sun6i-dma: Add burst case of 4

[Maxime Ripard]

On Sun, Oct 23, 2016 at 06:31:07PM +0200, Jean-Francois Moine wrote:
> On Tue, 4 Oct 2016 18:55:54 +0200
> Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > On Tue, Oct 04, 2016 at 12:40:11PM +0200, Jean-Francois Moine wrote:
> > > On Tue,  4 Oct 2016 11:46:14 +0200
> > > Mylène Josserand <mylene.josserand@xxxxxxxxxxxxxxxxxx> wrote:
> > > 
> > > > Add the case of a burst of 4 which is handled by the SoC.
> > > > 
> > > > Signed-off-by: Mylène Josserand <mylene.josserand@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >  drivers/dma/sun6i-dma.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> > > > index 8346199..0485204 100644
> > > > --- a/drivers/dma/sun6i-dma.c
> > > > +++ b/drivers/dma/sun6i-dma.c
> > > > @@ -240,6 +240,8 @@ static inline s8 convert_burst(u32 maxburst)
> > > >  	switch (maxburst) {
> > > >  	case 1:
> > > >  		return 0;
> > > > +	case 4:
> > > > +		return 1;
> > > >  	case 8:
> > > >  		return 2;
> > > >  	default:
> > > > -- 
> > > > 2.9.3
> > > 
> > > This patch has already been rejected by Maxime in the threads
> > > 	http://www.spinics.net/lists/dmaengine/msg08610.html
> > > and
> > > 	http://www.spinics.net/lists/dmaengine/msg08719.html
> > > 
> > > I hope you will find the way he wants for this maxburst to be added.
> > 
> > I was talking about something along these lines (not tested):
> 
> I wonder why you don't submit this yourself.

I thought you were the one who cared. You asked for what I had in
mind, here it is.

> > -------8<---------
> > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> > index 83461994e418..573ac4608293 100644
> > --- a/drivers/dma/sun6i-dma.c
> > +++ b/drivers/dma/sun6i-dma.c
> > @@ -240,6 +240,8 @@ static inline s8 convert_burst(u32 maxburst)
> >  	switch (maxburst) {
> >  	case 1:
> >  		return 0;
> > +	case 4:
> > +		return 1;
> >  	case 8:
> >  		return 2;
> >  	default:
> > @@ -1110,11 +1112,19 @@ static int sun6i_dma_probe(struct platform_device *pdev)
> >  	sdc->slave.dst_addr_widths		= BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
> >  						  BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
> >  						  BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
> > +	sdc->slave.dst_bursts			= BIT(1) | BIT(8);
> > +	sdc->slave.src_bursts			= BIT(1) | BIT(8);
> >  	sdc->slave.directions			= BIT(DMA_DEV_TO_MEM) |
> >  						  BIT(DMA_MEM_TO_DEV);
> >  	sdc->slave.residue_granularity		= DMA_RESIDUE_GRANULARITY_BURST;
> >  	sdc->slave.dev = &pdev->dev;
> >  
> > +	if (of_device_is_compatible(pdev->dev.of_node,
> > +				    "allwinner,sun8i-h3-dma")) {
> > +		sdc->slave.dst_bursts |= BIT(4);
> > +		sdc->slave.src_bursts |= BIT(4);
> > +	}
> > +
> >  	sdc->pchans = devm_kcalloc(&pdev->dev, sdc->cfg->nr_max_channels,
> >  				   sizeof(struct sun6i_pchan), GFP_KERNEL);
> >  	if (!sdc->pchans)
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index cc535a478bae..f7bbec24bb58 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -673,6 +673,8 @@ struct dma_filter {
> >   * 	each type of direction, the dma controller should fill (1 <<
> >   * 	<TYPE>) and same should be checked by controller as well
> >   * @max_burst: max burst capability per-transfer
> > + * @dst_bursts: bitfield of the available burst sizes for the destination
> > + * @src_bursts: bitfield of the available burst sizes for the source
> 
> You did not define dst_bursts nor src_bursts.
> 
> >   * @residue_granularity: granularity of the transfer residue reported
> >   *	by tx_status
> >   * @device_alloc_chan_resources: allocate resources and return the
> > @@ -800,6 +802,14 @@ struct dma_device {
> >  static inline int dmaengine_slave_config(struct dma_chan *chan,
> >  					  struct dma_slave_config *config)
> >  {
> > +	if (config->src_maxburst && config->device->src_bursts &&
> > +	    !(BIT(config->src_maxburst) & config->device->src_bursts))
> 
> The maxburst may be as big as 4Kibytes, then, I am not sure that this
> code will work!
> 
> > +		return -EINVAL;
> > +
> > +	if (config->dst_maxburst && config->device->dst_bursts &&
> > +	    !(BIT(config->dst_maxburst) & config->device->dst_bursts))
> > +		return -EINVAL;
> > +
> >  	if (chan->device->device_config)
> >  		return chan->device->device_config(chan, config);
> > -------8<------------ 
> 
> Yes, I know that the burst size is always a power of 2.
> The best way to check it would be to change the {src,dts}_maxburst to a
> bitmap of the possible bursts as 0x0d for 1,4 and 8 bytes. But this
> asks for a lot of changes...

To be honest, I'm not really a big fan of those tree wide changes
without any way to maintain compatibility. It ends up in a single,
huge patch if we want to maintain bisectability that just isn't
reviewable.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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