Re: [PATCH 07/10] NTB: epf: Make db_valid_mask cover only real doorbell bits

On Wed, Feb 25, 2026 at 09:47:43AM -0700, Dave Jiang wrote:
> 
> 
> On 2/24/26 6:34 AM, Koichiro Den wrote:
> > ndev->db_count includes an unused doorbell slot due to the legacy extra
> > offset in the peer doorbell path. db_valid_mask must cover only the real
> > doorbell bits and exclude the unused slot.
> > 
> > Set db_valid_mask to BIT_ULL(db_count - 1) - 1.
> > 
> > Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
> > Signed-off-by: Koichiro Den <[email protected]>
> > ---
> >  drivers/ntb/hw/epf/ntb_hw_epf.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> > index bce7130fec39..ee499eaed4f3 100644
> > --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> > +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> > @@ -580,7 +580,13 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
> >  		return ret;
> >  	}
> >  
> > -	ndev->db_valid_mask = BIT_ULL(ndev->db_count) - 1;
> > +	if (ndev->db_count < NTB_EPF_MIN_DB_COUNT) {
> > +		dev_err(dev, "db_count %u is less than %u\n", ndev->db_count,
> > +			NTB_EPF_MIN_DB_COUNT);
> > +		return -EINVAL;
> > +	}
> > +
> > +	ndev->db_valid_mask = BIT_ULL(ndev->db_count - 1) - 1;
> 
> I would suggest adding a comment in the code for why this is for future readers.

Will do in v2. Thanks for the suggestion.

Koichiro

> 
> DJ
> 
> >  	ndev->mw_count = readl(ndev->ctrl_reg + NTB_EPF_MW_COUNT);
> >  	ndev->spad_count = readl(ndev->ctrl_reg + NTB_EPF_SPAD_COUNT);
> >  
>