netdev - RE: [PATCH RFC 24/30] net: fec: better implementation of iMX6 ERR006358 quirk

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Date:	Wed, 25 Jun 2014 01:41:21 +0000
From:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH RFC 24/30] net: fec: better implementation of iMX6
	ERR006358 quirk

From: Russell King - ARM Linux <linux@....linux.org.uk> Data: Tuesday, June 24, 2014 6:29 PM
>To: Duan Fugang-B38611
>Cc: netdev@...r.kernel.org; linux-arm-kernel@...ts.infradead.org
>Subject: Re: [PATCH RFC 24/30] net: fec: better implementation of iMX6
>ERR006358 quirk
>
>On Sun, Jun 22, 2014 at 09:49:11AM +0100, Russell King - ARM Linux wrote:
>> On Sun, Jun 22, 2014 at 08:38:49AM +0000, fugang.duan@...escale.com
>wrote:
>> > From: Russell King - ARM Linux <linux@....linux.org.uk> Data:
>> > Sunday, June 22, 2014 4:13 PM
>> > >To: Duan Fugang-B38611
>> > >Cc: linux-arm-kernel@...ts.infradead.org; netdev@...r.kernel.org
>> > >Subject: Re: [PATCH RFC 24/30] net: fec: better implementation of
>> > >iMX6
>> > >ERR006358 quirk
>> > >
>> > >On Sun, Jun 22, 2014 at 07:49:11AM +0000, fugang.duan@...escale.com
>wrote:
>> > >> From: Russell King <rmk@....linux.org.uk> Data: Friday, June 20,
>> > >> 2014
>> > >> 8:14 PM
>> > >> >To: linux-arm-kernel@...ts.infradead.org
>> > >> >Cc: Duan Fugang-B38611; netdev@...r.kernel.org
>> > >> >Subject: [PATCH RFC 24/30] net: fec: better implementation of
>> > >> >iMX6
>> > >> >ERR006358 quirk
>> > >> >
>> > >> >+
>> > >> >+	/* ERR006538: Keep the transmitter going */
>> > >> >+	if (fep->dirty_tx != fep->cur_tx &&
>> > >> >+	    readl(fep->hwp + FEC_X_DES_ACTIVE) == 0)
>> > >> >+		writel(0, fep->hwp + FEC_X_DES_ACTIVE);
>> > >> > }
>> > >> >
>> ...
>> > >While I agree that we can read back to check whether the device
>> > >indicates that transmit is active, there's no point to the other
>> > >tests.  If there are entries in the transmit ring but the
>> > >transmitter indicates that it is not active, then it is obvious
>> > >that the bug has been hit.  This is exactly what my implementation
>above does.
>> > >
>> > The condition "fep->dirty_tx != fep->cur_tx" is not only limited for
>the errata.
>> > I mean only add extra trigger TDAR for the issue.
>>
>> Yes, I agree that test is wrong (that's what comes from shuffling the
>> patches... subsequent patches modify the indexing mechanism).  It
>> should
>> be:
>>
>>         if (bdp != fep->cur_tx &&
>>             readl(fep->hwp + FEC_X_DES_ACTIVE) == 0)
>>                 writel(0, fep->hwp + FEC_X_DES_ACTIVE);
>>
>> Since "bdp" is the post-incremented dirty_tx pointer, which, when it
>> is equal to fep->cur_tx means that the ring is empty.
>
>Any further comments, or do I take the silence to mean that you agree with
>the above statement?  I would like to get this settled to I can spin v2 of
>this set.
>
>Thanks.
>
I agree your statement.

Thanks,
Andy
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