netdev - [PATCH net-next] r8169: work around an irq coalescing related tx timeout

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Message-ID: <14cfcad9-7298-f183-295e-63e13858b863@gmail.com>
Date:   Mon, 18 May 2020 22:45:10 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net-next] r8169: work around an irq coalescing related tx
 timeout

In [0] a user reported reproducible tx timeouts on RTL8168f except
PktCntrDisable is set and irq coalescing is enabled.
Realtek told me that they are not aware of any related hw issue on
this chip version, therefore root cause is still unknown. It's not
clear whether the issue affects one or more chip versions in general,
or whether issue is specific to reporter's system.
Due to this level of uncertainty, and due to the fact that I'm aware
of this one report only, let's apply the workaround on net-next only.
After this change setting irq coalescing via ethtool can reliably
avoid the issue on the affected system.

[0] https://bugzilla.kernel.org/show_bug.cgi?id=207205

Reported-by: 
Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 23f150092..79817d4ff 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -1871,6 +1871,15 @@ static int rtl_set_coalesce(struct net_device *dev, struct ethtool_coalesce *ec)

 	RTL_W16(tp, IntrMitigate, w);

+	/* Meaning of PktCntrDisable bit changed from RTL8168e-vl */
+	if (rtl_is_8168evl_up(tp)) {
+		if (!rx_fr && !tx_fr)
+			/* disable packet counter */
+			tp->cp_cmd |= PktCntrDisable;
+		else
+			tp->cp_cmd &= ~PktCntrDisable;
+	}
+
 	tp->cp_cmd = (tp->cp_cmd & ~INTT_MASK) | cp01;
 	RTL_W16(tp, CPlusCmd, tp->cp_cmd);
 	rtl_pci_commit(tp);
-- 
2.26.2