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

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Message-ID: <yw1x7eyrlc3s.fsf@mansr.com>
Date:   Sat, 29 Jul 2017 12:24:39 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Mason <slash.tmp@...e.fr>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        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>
Subject: Re: [RFC PATCH v1] net: ethernet: nb8800: Reset HW block in ndo_open

Mason <slash.tmp@...e.fr> writes:

> On 28/07/2017 20:56, Måns Rullgård wrote:
>
>> Marc Gonzalez 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'll try adding delays in strategic places, and see if
> I can trigger the same bug on tango4. If I can't, then
> this work around is all we've got.
>
> And I need nb8800_init for resume anyway, so I might
> as well use it in ndo_open.
>
> TODO: test power savings from holding HW in reset.
>
>>> 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.
>
> I don't have always have time to figure out exactly how
> broken HW is broken. It's already bad enough that disabling
> DMA requires sending a fake packet through the loop back...

Until you figure out why it's getting stuck, we can't be sure it isn't
caused by something that could trigger at any time.

>>>> 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.
>
> The original code calls nb8800_pause_config() every
> time the link comes up. The proposed patch doesn't
> change that.

Yes, but by then you've reset those parameters to the defaults.

-- 
Måns Rullgård