netdev - Re: [RFC PATCH v1] net: ethernet: nb8800: Reset HW block in ndo

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Message-ID: <yw1xfudgl7am.fsf@mansr.com>
Date:   Fri, 28 Jul 2017 19:56:17 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mason <slash.tmp@...e.fr>
Subject: Re: [RFC PATCH v1] net: ethernet: nb8800: Reset HW block in ndo_open

Marc Gonzalez <marc_gonzalez@...madesigns.com> writes:

> On 28/07/2017 18:17, Måns Rullgård wrote:
>
>> Marc Gonzalez wrote:
>> 
>>> ndo_stop breaks RX in a way that ndo_open is unable to undo.
>> 
>> Please elaborate.  Why can't it be fixed in a less heavy-handed way?
>
> I'm not sure what "elaborate" means. After we've been through
> ndo_stop once, the board can send packets, but it doesn't see
> any replies from remote systems. RX is wedged.

So you say, but you have not explained why this happens.  Until we know
why, we can't decide on the proper fix.

> I think ndo_stop is rare enough an event that doing a full
> reset is not an issue, in terms of performance.

Performance isn't the issue.  Doing the right thing is.

> Also I will need this infrastructure anyway for suspend/resume
> support.

> It might also make sense to put the HW in reset at close
> (to save power). I will try measuring the power savings,
> if any.
>
>>> Work around the issue by resetting the HW in ndo_open.
>>> This will provide the basis for suspend/resume support.
>>>
>>> Signed-off-by: Marc Gonzalez <marc_gonzalez@...madesigns.com>
>>> ---
>>>  drivers/net/ethernet/aurora/nb8800.c | 40 +++++++++++++++++-------------------
>>>  drivers/net/ethernet/aurora/nb8800.h |  1 +
>>>  2 files changed, 20 insertions(+), 21 deletions(-)
>> 
>> I'm pretty sure this doesn't preserve everything it should.
>
> Hmmm, we're supposed to start fresh ("full reset").
> What could there be to preserve?
> You mentioned flow control and multicast elsewhere.
> I will take a closer look. Thanks for the heads up.

Yes, those settings are definitely lost with your patch.  Now I'm not
sure whether the networking core expects these to survive a stop/start
cycle, so please check that.  There might also be other less obvious
things that need to be preserved.

-- 
Måns Rullgård