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Subject: Re: [PATCH v3 2/4] net: nb8800: Simplify nb8800_pause_config()
Date: Tue, 14 Nov 2017 13:22:50 +0000
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Cc: David Miller <davem@davemloft.net>,
        netdev <netdev@vger.kernel.org>,
        "Linux ARM" <linux-arm-kernel@lists.infradead.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Thibaud Cornic <thibaud_cornic@sigmadesigns.com>,
        Mason <slash.tmp@free.fr>
To: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
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In-Reply-To: <569542b1-8e56-d7da-f7a0-affd89bfed62@sigmadesigns.com> (Marc
        Gonzalez's message of "Tue, 14 Nov 2017 13:56:34 +0100")
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Marc Gonzalez <marc_gonzalez@sigmadesigns.com> writes:

> On 14/11/2017 13:38, Måns Rullgård wrote:
>
>> Marc Gonzalez writes:
>> 
>>> The "flow control enable" bit can be tweaked, even if DMA is enabled.
>> 
>> No, it can't.  Maybe on some of your newer chips it can, but not on the
>> older ones.
>
> Again, I suppose you are referring to your SMP8642-based board.
>
> Are you saying you tested this patch, and it doesn't work?
> What are the symptoms?

I didn't test that patch per se.  I did initially try simply changing
that bit, and this didn't work.  Either it had no effect, or it locked
up the controller, I forget which.  The manual explicitly states that
writes are forbidden while the DMA enabled bit is set.

If shutting down the DMA really isn't possible, I would rather just
allow changing the flow control setting only when the interface is
stopped.  The normal case of getting the initial setting from the
auto-negotiation will still work properly.  It just won't be possible to
change it while the link is active.

-- 
Måns Rullgård