Re: [RFC net-next v3 4/7] net/mlx5e: add op for getting netdev DMA device

[Mina Almasry <almasrymina@google.com>]

On Mon, Aug 18, 2025 at 10:40 AM Dragos Tatulea <dtatulea@nvidia.com> wrote:
>
> On Fri, Aug 15, 2025 at 10:37:15AM -0700, Mina Almasry wrote:
> > On Fri, Aug 15, 2025 at 4:07 AM Dragos Tatulea <dtatulea@nvidia.com> wrote:
> > >
> > > For zero-copy (devmem, io_uring), the netdev DMA device used
> > > is the parent device of the net device. However that is not
> > > always accurate for mlx5 devices:
> > > - SFs: The parent device is an auxdev.
> > > - Multi-PF netdevs: The DMA device should be determined by
> > >   the queue.
> > >
> > > This change implements the DMA device queue API that returns the DMA
> > > device appropriately for all cases.
> > >
> > > Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> > > ---
> > >  .../net/ethernet/mellanox/mlx5/core/en_main.c | 24 +++++++++++++++++++
> > >  1 file changed, 24 insertions(+)
> > >
> > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > > index 21bb88c5d3dc..0e48065a46eb 100644
> > > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > > @@ -5625,12 +5625,36 @@ static int mlx5e_queue_start(struct net_device *dev, void *newq,
> > >         return 0;
> > >  }
> > >
> > > +static struct device *mlx5e_queue_get_dma_dev(struct net_device *dev,
> > > +                                             int queue_index)
> > > +{
> > > +       struct mlx5e_priv *priv = netdev_priv(dev);
> > > +       struct mlx5e_channels *channels;
> > > +       struct device *pdev = NULL;
> > > +       struct mlx5e_channel *ch;
> > > +
> > > +       channels = &priv->channels;
> > > +
> > > +       mutex_lock(&priv->state_lock);
> > > +
> > > +       if (queue_index >= channels->num)
> > > +               goto out;
> > > +
> > > +       ch = channels->c[queue_index];
> > > +       pdev = ch->pdev;
> >
> > This code assumes priv is initialized, and probably that the device is
> > up/running/registered. At first I thought that was fine, but now that
> > I look at the code more closely, netdev_nl_bind_rx_doit checks if the
> > device is present but doesn't seem to check that the device is
> > registered.
> >
> > I wonder if we should have a generic check in netdev_nl_bind_rx_doit
> > for NETDEV_REGISTERED, and if not, does this code handle unregistered
> > netdev correctly (like netdev_priv and priv->channels are valid even
> > for unregistered mlx5 devices)?
> >
> netdev_get_by_index_lock() returns non-NULL only when the device is in
> state NETDEV_REGISTERED or NETREG_UNINITIALIZED. So I think  that this
> check should suffice.
>

Ack, thanks for checking. For the patch:

Reviewed-by: Mina Almasry <almasrymina@google.com>



-- 
Thanks,
Mina