netdev - Re: [PATCH net 2/2] net: systemport: fix UniMAC reset logic

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Message-ID: <CAGVrzcaquiXbkt0HtEuyOqq+9os+5P8Hh=UezFdmNZo=w=LZYQ@mail.gmail.com>
Date:	Tue, 24 Jun 2014 16:16:16 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 2/2] net: systemport: fix UniMAC reset logic

2014-06-24 16:12 GMT-07:00 David Miller <davem@...emloft.net>:
> From: Florian Fainelli <f.fainelli@...il.com>
> Date: Fri, 20 Jun 2014 13:01:40 -0700
>
>> The UniMAC CMD_SW_RESET bit is not a self-clearing bit, so we need to
>> assert it, wait a bit and clear it manually. As a result, umac_reset()
>> is updated not to return any value.
>>
>> By setting CMD_SW_RESET and only that bit, we were also clearing the
>> other 31 bits, overriding the hardware reset defaults which are
>> correctly set on purpose.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>
> I agree with Sergei, this is really suspicious that the existing code
> never wrote the sw reset bit into the register at all, it just writes
> a zero.
>
> And you don't mention this at all in this commit message.
>
> If I were to guess, I would fathom that the sequence was partially
> copied from the other broadcom driver, the genet one.  There it
> issues CMD_SW_RESET by first clearing the entire regiser to zero,
> then writing CMD_SW_RESET, and then polling for that bit to clear.
>
> I'm assuming that is being done for a good reason, and I'd like
> you to make sure that same reason does not apply here.

I'll resubmit with a proper explanation, thanks.
-- 
Florian
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