linux-kernel - Re: [EXTERNAL] Re: [PATCH] net: phy: dp83867: perform soft reset and retain established link

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Date:   Fri, 28 May 2021 18:52:39 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     "Bajjuri, Praneeth" <praneeth@...com>
Cc:     "Modi, Geet" <geet.modi@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXTERNAL] Re: [PATCH] net: phy: dp83867: perform soft reset and
 retain established link

On Fri, May 28, 2021 at 11:32:15AM -0500, Bajjuri, Praneeth wrote:
> Hi Andrew,
> 
> On 3/31/2021 11:35 AM, Andrew Lunn wrote:
> > >      > as per datasheet: https://www.ti.com/lit/ds/symlink/dp83867cr.pdf
> > > 
> > >      > 8.6.26 Control Register (CTRL)
> > >      > do SW_RESTART to perform a reset not including the registers and is
> > >      > acceptable to do this if a link is already present.
> > > 
> > > 
> > >      I don't see any code here to determine if the like is present. What if
> > >      the cable is not plugged in?
> > > 
> > >      This API is primarily used for reset. Link Status is checked thru different
> > > register. This shall not impact the cable plug in/out. With this change, it
> > > will align with DP83822 driver API.
> > 
> > So why is there the comment:
> > 
> > >      >                                            and is
> > >      > acceptable to do this if a link is already present.
> > 
> > That kind of says, it is not acceptable to do this if the link is not
> > present. Which is why i'm asking.
> 
> Does the feedback from Geet help in clarity you requested.
> Ref:
> https://lore.kernel.org/netdev/4838EA12-7BF4-4FF2-8305-7446C3498DDF@ti.com/

Not really.

>                                                        and is
> > >      > acceptable to do this if a link is already present.

There needs to be something to either:

1) Ensure there is link, so we known we are within acceptable
behaviour.

2) Document what happens when there is no link, meaning we do
something which is not acceptable. Is the magic smoke going to be
released? Does the link die until the next reboot? Or despite it being
unacceptable, nothing really happens, and it is not a problem?

	      Andrew