netdev - [PATCH 1/1] net: socionext: clear rx irq correctly

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Message-Id: <1539260906-29596-1-git-send-email-ilias.apalodimas@linaro.org>
Date:   Thu, 11 Oct 2018 15:28:26 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     netdev@...r.kernel.org, jaswinder.singh@...aro.org
Cc:     ard.biesheuvel@...aro.org, masami.hiramatsu@...aro.org,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: [PATCH 1/1] net: socionext: clear rx irq correctly

commit 63ae7949e94a ("net: socionext: Use descriptor info instead of MMIO reads on Rx")
removed constant mmio reads from the driver and started using a descriptor 
field to check if packet should be processed.
This lead the napi rx handler being constantly called while no packets
needed processing and ksoftirq getting 100% cpu usage. Issue one mmio read 
to clear the irq correcty after processing packets

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Reported-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 drivers/net/ethernet/socionext/netsec.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
index 7aa5ebb..4289ccb 100644
--- a/drivers/net/ethernet/socionext/netsec.c
+++ b/drivers/net/ethernet/socionext/netsec.c
@@ -735,8 +735,11 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
 		u16 idx = dring->tail;
 		struct netsec_de *de = dring->vaddr + (DESC_SZ * idx);
 
-		if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD))
+		if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD)) {
+			/* reading the register clears the irq */
+			netsec_read(priv, NETSEC_REG_NRM_RX_PKTCNT);
 			break;
+		}
 
 		/* This  barrier is needed to keep us from reading
 		 * any other fields out of the netsec_de until we have
-- 
2.7.4