[PATCH v2] net: macb: restart tx after tx used bit read

[PATCH v2] net: macb: restart tx after tx used bit read

[Claudiu.Beznea]

From: Claudiu Beznea <claudiu.beznea@microchip.com>

On some platforms (currently detected only on SAMA5D4) TX might stuck
even the pachets are still present in DMA memories and TX start was
issued for them. This happens due to race condition between MACB driver
updating next TX buffer descriptor to be used and IP reading the same
descriptor. In such a case, the "TX USED BIT READ" interrupt is asserted.
GEM/MACB user guide specifies that if a "TX USED BIT READ" interrupt
is asserted TX must be restarted. Restart TX if used bit is read and
packets are present in software TX queue. Packets are removed from software
TX queue if TX was successful for them (see macb_tx_interrupt()).

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
---

changes in v2:
- use "static inline" instead of "inline static" for macb_tx_restart()

 drivers/net/ethernet/cadence/macb_main.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 1d86b4d5645a..f920230386ee 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -61,7 +61,8 @@
 #define MACB_TX_ERR_FLAGS	(MACB_BIT(ISR_TUND)			\
 					| MACB_BIT(ISR_RLE)		\
 					| MACB_BIT(TXERR))
-#define MACB_TX_INT_FLAGS	(MACB_TX_ERR_FLAGS | MACB_BIT(TCOMP))
+#define MACB_TX_INT_FLAGS	(MACB_TX_ERR_FLAGS | MACB_BIT(TCOMP)	\
+					| MACB_BIT(TXUBR))
 
 /* Max length of transmit frame must be a multiple of 8 bytes */
 #define MACB_TX_LEN_ALIGN	8
@@ -1312,6 +1313,21 @@ static void macb_hresp_error_task(unsigned long data)
 	netif_tx_start_all_queues(dev);
 }
 
+static inline void macb_tx_restart(struct macb_queue *queue)
+{
+	unsigned int head = queue->tx_head;
+	unsigned int tail = queue->tx_tail;
+	struct macb *bp = queue->bp;
+
+	if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
+		queue_writel(queue, ISR, MACB_BIT(TXUBR));
+
+	if (head == tail)
+		return;
+
+	macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(TSTART));
+}
+
 static irqreturn_t macb_interrupt(int irq, void *dev_id)
 {
 	struct macb_queue *queue = dev_id;
@@ -1369,6 +1385,9 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
 		if (status & MACB_BIT(TCOMP))
 			macb_tx_interrupt(queue);
 
+		if (status & MACB_BIT(TXUBR))
+			macb_tx_restart(queue);
+
 		/* Link change detection isn't possible with RMII, so we'll
 		 * add that if/when we get our hands on a full-blown MII PHY.
 		 */
-- 
2.7.4

Re: [PATCH v2] net: macb: restart tx after tx used bit read

[David Miller]

From: <Claudiu.Beznea@microchip.com>
Date: Fri, 14 Dec 2018 10:40:47 +0000

> From: Claudiu Beznea <claudiu.beznea@microchip.com>
> 
> On some platforms (currently detected only on SAMA5D4) TX might stuck
> even the pachets are still present in DMA memories and TX start was
> issued for them. This happens due to race condition between MACB driver
> updating next TX buffer descriptor to be used and IP reading the same
> descriptor. In such a case, the "TX USED BIT READ" interrupt is asserted.
> GEM/MACB user guide specifies that if a "TX USED BIT READ" interrupt
> is asserted TX must be restarted. Restart TX if used bit is read and
> packets are present in software TX queue. Packets are removed from software
> TX queue if TX was successful for them (see macb_tx_interrupt()).
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
> ---
> 
> changes in v2:
> - use "static inline" instead of "inline static" for macb_tx_restart()

Yes that is the correct order for a static inline function declaration,
but in foo.c files we do not use the inline keyword and instead let the
compiler decide the best thing to do.

Please remove this inline keyword and resubmit.

Thank you.