Re: [PATCH v2 09/15] DMA: shdma: support referencing specific DMACs within a multiplexer in DT

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

Hi Laurent

Thanks for the comments

On Mon, 22 Jul 2013, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> Thanks for the patch.
> 
> On Friday 19 July 2013 18:29:34 Guennadi Liakhovetski wrote:
> > Currently shdma DT nodes have to be placed under a multiplexer node. DMA
> > slave DT nodes then use that multiplexer's phandle in their "dmas"
> > properties. However, sometimes it can be necessary to let DMA slaves only
> > use a specific DMAC instance. In this case it would be logical to just use
> > the respective phandle in that slave's "dmas" property. For this to work
> > the referenced DMAC has to register a struct of_dma instance, which isn't
> > presently done. Instead the driver currently only registers one struct
> > of_dma for the multiplexer. This patch adds support for such
> > configurations. To enable this option a "#dma-cells" property also must be
> > added to the respective DMAC DT node.
> > 
> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
> > ---
> >  Documentation/devicetree/bindings/dma/shdma.txt |   16 ++++++
> 
> Patches that touch DT bindings must be CC'ed to devicetree@vger.kernel.org 
> (http://www.gossamer-threads.com/lists/linux/kernel/1750512).

Yes, I saw that announcements, but if my calculations are correct, these 
patches went out before the MAINTAINERS patch above hit the mailing list, 
and as of this writing it's still not in next.

> >  drivers/dma/sh/shdma.h                          |    7 +++
> >  drivers/dma/sh/shdmac.c                         |   66 ++++++++++++++++++++
> >  3 files changed, 89 insertions(+), 0 deletions(-)

[snip]

> > diff --git a/drivers/dma/sh/shdmac.c b/drivers/dma/sh/shdmac.c
> > index ae89261..0ddcddf 100644
> > --- a/drivers/dma/sh/shdmac.c
> > +++ b/drivers/dma/sh/shdmac.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> >  #include <linux/of_device.h>
> > +#include <linux/of_dma.h>
> >  #include <linux/slab.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/dmaengine.h>
> > @@ -665,6 +666,63 @@ static const struct shdma_ops sh_dmae_shdma_ops = {
> >  	.get_partial = sh_dmae_get_partial,
> >  };
> > 
> > +static bool sh_dmae_chan_filter(struct dma_chan *chan, void *arg)
> > +{
> > +	struct sh_dmae_filter_info *info = arg;
> > +	struct shdma_chan *schan = to_shdma_chan(chan);
> > +	int match = info->hw_req;
> > +
> > +	if (match < 0)
> > +		/* No slave requested - arbitrary channel */
> > +		return true;
> > +
> > +	dev_dbg(schan->dev, "%s(): trying %s for 0x%x\n", __func__,
> > +		info->of_node->full_name, match);
> > +
> > +	if (schan->dev->of_node != info->of_node)
> > +		return false;
> > +
> > +	return !sh_dmae_set_slave(schan, match, true);
> > +}
> > +
> > +static struct dma_chan *sh_dmae_of_xlate(struct of_phandle_args *dma_spec,
> > +					 struct of_dma *ofdma)
> > +{
> > +	struct sh_dmae_filter_info *info = ofdma->of_dma_data;
> > +	u32 id = dma_spec->args[0];
> > +	dma_cap_mask_t mask;
> > +	struct dma_chan *chan;
> > +
> > +	if (dma_spec->args_count != 1)
> > +		return NULL;
> > +
> > +	dma_cap_zero(mask);
> > +	/* Only slave DMA channels can be allocated via DT */
> > +	dma_cap_set(DMA_SLAVE, mask);
> > +
> > +	info->hw_req = id;
> > +	info->of_node = dma_spec->np;
> > +
> > +	chan = dma_request_channel(mask, sh_dmae_chan_filter, info);
> > +	if (chan)
> > +		to_shdma_chan(chan)->hw_req = id;
> > +
> > +	return chan;
> > +}
> 
> Would https://lkml.org/lkml/2013/3/25/250 help ?

Don't think so. In my .xlate() method I also assign the .hw_req field, and 
the filter is pretty different. And in any case that patch is from 
March... And I don't see it in the mainline or in next, are there plans to 
re-push it?

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/