netdev - Re: [PATCH v3 3/4] net: nb8800: Move HW init to ndo

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Message-ID: <30042004-4e13-b7e2-b49d-754db54cc5ce@sigmadesigns.com>
Date:   Tue, 14 Nov 2017 17:41:09 +0100
From:   Marc Gonzalez <marc_gonzalez@...madesigns.com>
To:     Mans Rullgard <mans@...sr.com>
CC:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        "Linux ARM" <linux-arm-kernel@...ts.infradead.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH v3 3/4] net: nb8800: Move HW init to ndo_open()

On 14/11/2017 14:54, Måns Rullgård wrote:

> Marc Gonzalez writes:
> 
>> On 14/11/2017 13:40, Måns Rullgård wrote:
>>
>>> Marc Gonzalez wrote:
>>>
>>>> Power entire ethernet block down in ndo_stop().
>>>> Power it back up in ndo_open() and perform HW init.
>>>> Delete nb8800_dma_stop.
>>>
>>> Leave it alone, please.  Not all chips might have a separate power
>>> domain for this.  Also, it works just fine on the older chips.
>>
>> There is no need for separate power domains. The ethernet block is
>> clock-gated when it is held in reset.
> 
> So you're not powering it down then.  Please be accurate.

Smirk. That looks like trolling.


>> The reset register is implemented on all tango3, tango4, tango5 chips.
> 
> It's still not a core feature.

Correct. But it covers 100% of all chips using this driver.
There is no point in trying to implement support for chips that
have never existed, do not exist, and never will.


>> nb8800_dma_stop() is a hack.
> 
> The hack originated from your company.

So why are you so insistent that we keep using it?


>> The HW dev has stated that it is not supported.  One cannot conclude
>> that it "works fine" just because you've never triggered the error
>> condition. (On tango5, the error condition triggers systematically.)
> 
> That sounds like a problem for tango5.

tango5 does have its share of issues.


> Also, I have repeated asked you what happens if the tango5 runs out of
> DMA buffers under normal operation.  Does that also cause it to lock up?
> If so, you have a much bigger problem on your hands.

I will run iperf3 tests with RX_DESC_COUNT lowered to 2.
Would that produce conclusive results?
Do you have other suggestions?


>> We have several customer bug reports on tango3 and tango4 chips complaining
>> about "broken" ethernet after a link down / link up cycle. They are using a
>> different driver, but it implements the same hack in enet_stop_rx().
>> There is a high probability that the DMA hack is responsible, and wedged the
>> RX DMA state machine.
> 
> But you have no idea what's really the problem?

I have an idea that enet_stop_rx() wedged the RX DMA state machine.