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

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Message-ID: <20140624102912.GM32514@n2100.arm.linux.org.uk>
Date:	Tue, 24 Jun 2014 11:29:12 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
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

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.

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