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

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Date:   Tue, 14 Nov 2017 14:26:29 +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 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. The reset register is implemented
on all tango3, tango4, tango5 chips.

nb8800_dma_stop() is a hack. 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.)

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.

Since older chips do support the reset register, this patch implements
the same method for all tango chips.