netdev - Re: [PATCH 12/15] habanalabs/gaudi: add debugfs entries for the NIC

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Message-ID: <20200914095018.21808fae@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 14 Sep 2020 09:50:18 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Omer Shpigelman <oshpigelman@...ana.ai>
Cc:     Oded Gabbay <oded.gabbay@...il.com>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        SW_Drivers <SW_Drivers@...ana.ai>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 12/15] habanalabs/gaudi: add debugfs entries for the NIC

On Mon, 14 Sep 2020 13:48:14 +0000 Omer Shpigelman wrote:
> On Thu, Sep 10, 2020 at 11:31 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > On Thu, 10 Sep 2020 23:17:59 +0300 Oded Gabbay wrote:  
> > > > Doesn't seem like this one shows any more information than can be
> > > > queried with ethtool, right?  
> > > correct, it just displays it in a format that is much more readable  
> > 
> > You can cat /sys/class/net/$ifc/carrier if you want 0/1.
> >   
> > > > > nic_mac_loopback
> > > > > is to set a port to loopback mode and out of it. It's not really
> > > > > configuration but rather a mode change.  
> > > >
> > > > What is this loopback for? Testing?  
> > >
> > > Correct.  
> > 
> > Loopback test is commonly implemented via ethtool -t  
> 
> This debugfs entry is only to set the port to loopback mode, not running a loopback test.
> Hence IMO adding a private flag is more suitable here and please correct me if I'm wrong.
> But either way, doing that from ethtool instead of debugfs is not a good practice in our case.
> Due to HW limitations, when we switch a port to/from loopback mode, we need to reset the device.
> Since ethtool works on specific interface rather than an entire device, we'll need to reset the device 10 times in order to switch the entire device to loopback mode.
> Moreover, running this command for one interface affects other interfaces which is not desirable when using ethtool AFAIK.
> Is there any other acceptable debugfs-like mechanism for that?

What's the use for a networking device which only communicates with
itself, other than testing?