RE: [PATCH v2 1/4] dmaengine: sf-pdma: Support of_dma_controller_register()

[<Shravan.Chippa@xxxxxxxxxxxxx>]

Hi,

> -----Original Message-----
> From: Samuel Holland <samuel.holland@xxxxxxxxxx>
> Sent: Wednesday, October 18, 2023 12:03 AM
> To: shravan Chippa - I35088 <Shravan.Chippa@xxxxxxxxxxxxx>;
> green.wan@xxxxxxxxxx; vkoul@xxxxxxxxxx; robh+dt@xxxxxxxxxx;
> krzysztof.kozlowski+dt@xxxxxxxxxx; palmer@xxxxxxxxxxx;
> paul.walmsley@xxxxxxxxxx; conor+dt@xxxxxxxxxx
> Cc: dmaengine@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-
> riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Nagasuresh Relli -
> I67208 <Nagasuresh.Relli@xxxxxxxxxxxxx>; Praveen Kumar - I30718
> <Praveen.Kumar@xxxxxxxxxxxxx>
> Subject: Re: [PATCH v2 1/4] dmaengine: sf-pdma: Support
> of_dma_controller_register()
> 
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> 
> Hi,
> 
> On 2023-10-02 11:22 PM, shravan chippa wrote:
> > From: Shravan Chippa <shravan.chippa@xxxxxxxxxxxxx>
> >
> > Update sf-pdma driver to adopt generic DMA device tree bindings.
> > It calls of_dma_controller_register() with sf-pdma specific
> > of_dma_xlate to get the generic DMA device tree helper support and the
> > DMA clients can look up the sf-pdma controller using standard APIs.
> >
> > Signed-off-by: Shravan Chippa <shravan.chippa@xxxxxxxxxxxxx>
> > ---
> >  drivers/dma/sf-pdma/sf-pdma.c | 44
> > +++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> >
> > diff --git a/drivers/dma/sf-pdma/sf-pdma.c
> > b/drivers/dma/sf-pdma/sf-pdma.c index d1c6956af452..06a0912a12a1
> > 100644
> > --- a/drivers/dma/sf-pdma/sf-pdma.c
> > +++ b/drivers/dma/sf-pdma/sf-pdma.c
> > @@ -20,6 +20,7 @@
> >  #include <linux/mod_devicetable.h>
> >  #include <linux/dma-mapping.h>
> >  #include <linux/of.h>
> > +#include <linux/of_dma.h>
> >  #include <linux/slab.h>
> >
> >  #include "sf-pdma.h"
> > @@ -490,6 +491,33 @@ static void sf_pdma_setup_chans(struct sf_pdma
> *pdma)
> >       }
> >  }
> >
> > +static struct dma_chan *sf_pdma_of_xlate(struct of_phandle_args
> *dma_spec,
> > +                                      struct of_dma *ofdma) {
> > +     struct sf_pdma *pdma = ofdma->of_dma_data;
> > +     struct device *dev = pdma->dma_dev.dev;
> > +     struct sf_pdma_chan  *chan;
> > +     struct dma_chan *c;
> > +     u32 channel_id;
> > +
> > +     if (dma_spec->args_count != 1) {
> > +             dev_err(dev, "Bad number of cells\n");
> > +             return NULL;
> > +     }
> > +
> > +     channel_id = dma_spec->args[0];
> > +
> > +     chan = &pdma->chans[channel_id];
> > +
> > +     c = dma_get_slave_channel(&chan->vchan.chan);
> 
> This does not look right to me. All of the channels in the controller are identical
> and support arbitrary addresses, so there is no need to use a specific physical
> channel. And unless Microchip has added something on top, the only way to
> trigger a transfer is through the MMIO interface, so there is no request ID to
> differentiate virtual channels either.
> 
> So it seems to me that #dma-cells should really be 0, and this function should
> just call dma_get_any_slave_channel().
> 

Thanks for your comment, yes all the channels are identical.

I have tested with dma_get_any_slave_channel()
it is not working.

dma_get_any_slave_channel() function searching for the DMA channel which has "DMA_SLAVE" capabilities.
But sf-pdma has only "DMA_MEMCPY" capabilities. 

*****************************
struct dma_chan *dma_get_any_slave_channel(struct dma_device *device)
{
        dma_cap_zero(mask);
        dma_cap_set(DMA_SLAVE, mask);
        chan = find_candidate(device, &mask, NULL, NULL);
}
******************************

So "dma_request_chan()" function throws an error like "sf-pdma 3000000.dma-controller: No more channels available"


Thanks,
Shravan.

> Regards,
> Samuel
> 
> > +     if (!c) {
> > +             dev_err(dev, "No more channels available\n");
> > +             return NULL;
> > +     }
> > +
> > +     return c;
> > +}
> > +
> >  static int sf_pdma_probe(struct platform_device *pdev)  {
> >       struct sf_pdma *pdma;
> > @@ -563,7 +591,20 @@ static int sf_pdma_probe(struct platform_device
> *pdev)
> >               return ret;
> >       }
> >
> > +     ret = of_dma_controller_register(pdev->dev.of_node,
> > +                                      sf_pdma_of_xlate, pdma);
> > +     if (ret < 0) {
> > +             dev_err(&pdev->dev,
> > +                     "Can't register SiFive Platform OF_DMA. (%d)\n", ret);
> > +             goto err_unregister;
> > +     }
> > +
> >       return 0;
> > +
> > +err_unregister:
> > +     dma_async_device_unregister(&pdma->dma_dev);
> > +
> > +     return ret;
> >  }
> >
> >  static int sf_pdma_remove(struct platform_device *pdev) @@ -583,6
> > +624,9 @@ static int sf_pdma_remove(struct platform_device *pdev)
> >               tasklet_kill(&ch->err_tasklet);
> >       }
> >
> > +     if (pdev->dev.of_node)
> > +             of_dma_controller_free(pdev->dev.of_node);
> > +
> >       dma_async_device_unregister(&pdma->dma_dev);
> >
> >       return 0;