From: Nathan Sullivan <nathan.sullivan@ni.com>
Date: Wed, 13 May 2015 22:01:36 +0000 (-0500)
Subject: net: macb: Add better comment for RXUBR handling
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=86b5e7de07aa1abc87ecc40d2aca6070348e4469;p=linux-beck.git

net: macb: Add better comment for RXUBR handling

Describe the handler for RXUBR better with a new comment.

Signed-off-by: Nathan Sullivan <nathan.sullivan@ni.com>
Reviewied-by: Josh Cartwright <joshc@ni.com>
Reviewied-by: Ben Shelton <ben.shelton@ni.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
index 61aa570aad9a..5f10dfc631d7 100644
--- a/drivers/net/ethernet/cadence/macb.c
+++ b/drivers/net/ethernet/cadence/macb.c
@@ -1037,6 +1037,12 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
 		 * add that if/when we get our hands on a full-blown MII PHY.
 		 */
 
+		/* There is a hardware issue under heavy load where DMA can
+		 * stop, this causes endless "used buffer descriptor read"
+		 * interrupts but it can be cleared by re-enabling RX. See
+		 * the at91 manual, section 41.3.1 or the Zynq manual
+		 * section 16.7.4 for details.
+		 */
 		if (status & MACB_BIT(RXUBR)) {
 			ctrl = macb_readl(bp, NCR);
 			macb_writel(bp, NCR, ctrl & ~MACB_BIT(RE));