Re: [PATCH v7 10/10] NTB: ntb_hw_epf: Support DMA and MW sharing a BAR

[Koichiro Den]

On Wed, Oct 21, 2026 at 10:58:54AM -0500, Frank Li wrote:
> On Wed, Oct 21, 2026 at 01:22:29PM +0900, Koichiro Den wrote:
> > A vNTB endpoint can place DMA resources after an MW in the same BAR.
> > Limit the MW to the advertised boundary so clients cannot overwrite
> > those resources.
> >
> > Advertise this support in LINK_UP, including when DMA is unavailable.
> > Older endpoints ignore the argument.
> 
> if ignore it, any side effect? Does host DMA side use wrong memory region,
> which actually is not mapped by EP?

None. This only advertises the host's support for MW/DMA BAR sharing.
Without DMA metadata from the EP, the host does not initialize endpoint DMA.

JFTR, this is the case I described in the cover letter, see [1] below:

  EP                              | Old host     | New host
  --------------------------------+--------------+----------
  Old                             | OK           | OK [1]
  New (dma_bar = -1)              | OK           | OK
  New (dedicated DMA BAR)         | OK           | OK
  New (shared MW/DMA BAR)         | Rejected     | OK

I've retested the [1] case with R-Car S4 just in case ...

Best regards,
Koichiro Den

> 
> Frank
> 
> >
> > Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> > ---
> > Changes since v6:
> >   - Split from the BAR-sharing patch. (Frank)
> >   - Advertise MW/DMA BAR boundary support in LINK_UP.
> >
> >  drivers/ntb/hw/epf/ntb_hw_epf.c | 46 +++++++++++++++++++++++++++------
> >  1 file changed, 38 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> > index e0016128b95c..56185870cba9 100644
> > --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> > +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> > @@ -382,6 +382,23 @@ static int ntb_epf_mw_to_bar(struct ntb_epf_dev *ndev, int idx)
> >  	return ndev->barno_map[BAR_MW1 + idx];
> >  }
> >
> > +static resource_size_t ntb_epf_mw_offset(struct ntb_epf_dev *ndev, int idx)
> > +{
> > +	return !idx ? readl(ndev->ctrl_reg + NTB_EPF_CTRL(mw1_offset)) : 0;
> > +}
> > +
> > +static resource_size_t ntb_epf_mw_size(struct ntb_epf_dev *ndev, int bar)
> > +{
> > +	resource_size_t end;
> > +
> > +	end = pci_resource_len(ndev->ntb.pdev, bar);
> > +	/* The DMA submap offset marks the end of an MW sharing this BAR. */
> > +	if (ndev->dma.submap.size && ndev->dma.submap.bar == bar)
> > +		end = min(end, ndev->dma.submap.offset);
> > +
> > +	return end;
> > +}
> > +
> >  static int ntb_epf_mw_count(struct ntb_dev *ntb, int pidx)
> >  {
> >  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
> > @@ -420,7 +437,7 @@ static int ntb_epf_mw_get_align(struct ntb_dev *ntb, int pidx, int idx,
> >  		*size_align = 1;
> >
> >  	if (size_max)
> > -		*size_max = pci_resource_len(ndev->ntb.pdev, bar);
> > +		*size_max = ntb_epf_mw_size(ndev, bar);
> >
> >  	return 0;
> >  }
> > @@ -524,7 +541,8 @@ static int ntb_epf_link_enable(struct ntb_dev *ntb,
> >  	struct device *dev = ndev->dev;
> >  	int ret;
> >
> > -	ret = ntb_epf_send_command(ndev, EPF_NTB_COMMAND_LINK_UP, 0);
> > +	ret = ntb_epf_send_command(ndev, EPF_NTB_COMMAND_LINK_UP,
> > +				   EPF_NTB_LINK_UP_DMA_MW_SUPPORTED);
> >  	if (ret) {
> >  		dev_err(dev, "Fail to enable link\n");
> >  		return ret;
> > @@ -707,7 +725,7 @@ static int ntb_epf_mw_set_trans(struct ntb_dev *ntb, int pidx, int idx,
> >  	if (bar < 0)
> >  		return bar;
> >
> > -	mw_size = pci_resource_len(ntb->pdev, bar);
> > +	mw_size = ntb_epf_mw_size(ndev, bar);
> >
> >  	if (size > mw_size) {
> >  		dev_err(dev, "Size:%pa is greater than the MW size %pa\n",
> > @@ -739,21 +757,20 @@ static int ntb_epf_peer_mw_get_addr(struct ntb_dev *ntb, int idx,
> >  				    phys_addr_t *base, resource_size_t *size)
> >  {
> >  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
> > -	u32 offset = 0;
> > +	resource_size_t offset;
> >  	int bar;
> >
> > -	if (idx == 0)
> > -		offset = readl(ndev->ctrl_reg + NTB_EPF_CTRL(mw1_offset));
> > -
> >  	bar = ntb_epf_mw_to_bar(ndev, idx);
> >  	if (bar < 0)
> >  		return bar;
> >
> > +	offset = ntb_epf_mw_offset(ndev, idx);
> > +
> >  	if (base)
> >  		*base = pci_resource_start(ndev->ntb.pdev, bar) + offset;
> >
> >  	if (size)
> > -		*size = pci_resource_len(ndev->ntb.pdev, bar) - offset;
> > +		*size = ntb_epf_mw_size(ndev, bar) - offset;
> >
> >  	return 0;
> >  }
> > @@ -851,6 +868,7 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
> >  {
> >  	struct device *dev = ndev->dev;
> >  	int ret;
> > +	int i;
> >
> >  	ndev->mw_count = readl(ndev->ctrl_reg + NTB_EPF_CTRL(num_mws));
> >  	if (ndev->mw_count > NTB_EPF_MAX_MW_COUNT) {
> > @@ -862,6 +880,18 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
> >  		dev_err(dev, "Invalid endpoint DMA layout\n");
> >  		return ret;
> >  	}
> > +	if (ndev->dma.submap.size) {
> > +		for (i = 0; i < ndev->mw_count; i++) {
> > +			int bar = ntb_epf_mw_to_bar(ndev, i);
> > +
> > +			if (bar == ndev->dma.submap.bar &&
> > +			    ntb_epf_mw_size(ndev, bar) <=
> > +			    ntb_epf_mw_offset(ndev, i)) {
> > +				dev_err(dev, "Invalid DMA/MW boundary\n");
> > +				return -EINVAL;
> > +			}
> > +		}
> > +	}
> >
> >  	/* One Link interrupt and rest doorbell interrupt */
> >  	ret = ntb_epf_init_isr(ndev, NTB_EPF_MIN_DB_COUNT + 1,
> > --
> > 2.54.0
> >