netdev - [PATCH net-next 02/12] net: mscc: ocelot: only drain extraction queue on error

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Date:   Sat, 13 Feb 2021 02:14:02 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Richard Cochran <richardcochran@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        UNGLinuxDriver@...rochip.com
Subject: [PATCH net-next 02/12] net: mscc: ocelot: only drain extraction queue on error

From: Vladimir Oltean <vladimir.oltean@....com>

It appears that the intention of this snippet of code is to not exit
ocelot_xtr_irq_handler() while in the middle of extracting a frame.
The problem in extracting it word by word is that future extraction
attempts are really easy to get desynchronized, since the IRQ handler
assumes that the first 16 bytes are the IFH, which give further
information about the frame, such as frame length.

But during normal operation, "err" will not be 0, but 4, set from here:

		for (i = 0; i < OCELOT_TAG_LEN / 4; i++) {
			err = ocelot_rx_frame_word(ocelot, grp, true, &ifh[i]);
			if (err != 4)
				break;
		}

		if (err != 4)
			break;

In that case, draining the extraction queue is a no-op. So explicitly
make this code execute only on negative err.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/ethernet/mscc/ocelot_vsc7514.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mscc/ocelot_vsc7514.c b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
index 590297d5e144..d19efbe6ffd3 100644
--- a/drivers/net/ethernet/mscc/ocelot_vsc7514.c
+++ b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
@@ -701,7 +701,7 @@ static irqreturn_t ocelot_xtr_irq_handler(int irq, void *arg)
 		dev->stats.rx_packets++;
 	}
 
-	if (err)
+	if (err < 0)
 		while (ocelot_read(ocelot, QS_XTR_DATA_PRESENT) & BIT(grp))
 			ocelot_read_rix(ocelot, QS_XTR_RD, grp);
 
-- 
2.25.1