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

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Message-ID: <20140622084911.GD32514@n2100.arm.linux.org.uk>
Date:	Sun, 22 Jun 2014 09:49:11 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"netdev@...r.kernel.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 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.

-- 
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improving, and getting towards what was expected from it.
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