Re: [dpdk-dev] [PATCH 2/2] net/mlx5: avoid unbind step to enable switchdev mode

[Jan Viktorin <viktorin@cesnet.cz>]

Hello Salva,

On Mon, 15 Mar 2021 15:53:51 +0000
Slava Ovsiienko <viacheslavo@nvidia.com> wrote:

> Hi, Jan
> 
> Yes, bullet [4] explicitly requires to unbind VFs, and detach the netdevs from the mlx5_core driver.
> Otherwise, kernel driver refuses to be configured with switchdev mode in [5]. So, [4] can't be skipped.
> After setting swithdev mode, VFs can be bound back (if it is needed, and these ones are not mapped to VMs):

OK, but I believe that it is **not possible** to follow the rule [5].
The guide explicitly says in [4] "can be rebind **after** the switchdev mode".
Just, if you unbind the device, there is no way how to configure the switchdev mode,
this is the contradiction I mentioned in the commit. You cannot configure switchdev
mode because the interface is gone and the path /sys/class/net/<net device>/compat/devlink/mode
no longer exists.

So, maybe, just the formulation is wrong. So, what is the **exact
right** way how to do it? I would change the commit accordingly. Just,
let's make it right. Would it work this way?

 # echo -n "<device pci address>" > /sys/bus/pci/drivers/mlx5_core/unbind
 # echo -n "<device pci address>" > /sys/bus/pci/drivers/mlx5_core/bind
 # echo switchdev > /sys/class/net/<net device>/compat/devlink/mode

It is good to mention that after the rebind, the <net device> can
change.

Regards,
Jan

> 
> echo -n "<device pci address>" > > /sys/bus/pci/drivers/mlx5_core/bind
> 
> With best regards,
> Slava
> 
> > -----Original Message-----
> > From: Jan Viktorin <iviktorin@fit.vutbr.cz>
> > Sent: Monday, March 15, 2021 17:34
> > To: dev@dpdk.org
> > Cc: Jan Viktorin <viktorin@cesnet.cz>; Asaf Penso <asafp@nvidia.com>;
> > Shahaf Shuler <shahafs@nvidia.com>; Slava Ovsiienko
> > <viacheslavo@nvidia.com>; Matan Azrad <matan@nvidia.com>
> > Subject: [PATCH 2/2] net/mlx5: avoid unbind step to enable switchdev mode
> > 
> > From: Jan Viktorin <viktorin@cesnet.cz>
> > 
> > The step 4 is a contradiction. It advices to unbind the device from the
> > mlx5_core which removes the associated system network interface (e.g.
> > eth0). In the step 5, the same system network interface (e.g. eth0) is
> > required to exist.
> > 
> > Signed-off-by: Jan Viktorin <viktorin@cesnet.cz>
> > ---
> >  doc/guides/nics/mlx5.rst | 6 +-----
> >  1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst index
> > 0a2dc3dee..122d8e0fc 100644
> > --- a/doc/guides/nics/mlx5.rst
> > +++ b/doc/guides/nics/mlx5.rst
> > @@ -1370,11 +1370,7 @@ the DPDK application.
> > 
> >          echo <num of vfs > /sys/class/net/<net device>/device/sriov_numvfs
> > 
> > -4. Unbind the device (can be rebind after the switchdev mode)::
> > -
> > -        echo -n "<device pci address>" >
> > /sys/bus/pci/drivers/mlx5_core/unbind
> > -
> > -5. Enable switchdev mode::
> > +4. Enable switchdev mode::
> > 
> >          echo switchdev > /sys/class/net/<net device>/compat/devlink/mode
> > 
> > --
> > 2.30.1  
>