[PATCH v3 1/2] mwifiex: Read a PCI register after writing the TX ring write pointer

From: "Jonas Dreßler" <verdre@v0yd.nl>
To: Amitkumar Karwar <amitkarwar@gmail.com>,
	Ganapathi Bhat <ganapathi017@gmail.com>,
	Xinming Hu <huxinming820@gmail.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>
Cc: "Jonas Dreßler" <verdre@v0yd.nl>,
	"Tsuchiya Yuto" <kitakar@gmail.com>,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	"Maximilian Luz" <luzmaximilian@gmail.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Pali Rohár" <pali@kernel.org>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Johannes Berg" <johannes@sipsolutions.net>,
	"Brian Norris" <briannorris@chromium.org>,
	"David Laight" <David.Laight@ACULAB.COM>,
	stable@vger.kernel.org
Subject: [PATCH v3 1/2] mwifiex: Read a PCI register after writing the TX ring write pointer
Date: Mon, 11 Oct 2021 15:32:23 +0200	[thread overview]
Message-ID: <20211011133224.15561-2-verdre@v0yd.nl> (raw)
In-Reply-To: <20211011133224.15561-1-verdre@v0yd.nl>

On the 88W8897 PCIe+USB card the firmware randomly crashes after setting
the TX ring write pointer. The issue is present in the latest firmware
version 15.68.19.p21 of the PCIe+USB card.

Those firmware crashes can be worked around by reading any PCI register
of the card after setting that register, so read the PCI_VENDOR_ID
register here. The reason this works is probably because we keep the bus
from entering an ASPM state for a bit longer, because that's what causes
the cards firmware to crash.

This fixes a bug where during RX/TX traffic and with ASPM L1 substates
enabled (the specific substates where the issue happens appear to be
platform dependent), the firmware crashes and eventually a command
timeout appears in the logs.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=109681
Cc: stable@vger.kernel.org
Signed-off-by: Jonas Dreßler <verdre@v0yd.nl>
---
 drivers/net/wireless/marvell/mwifiex/pcie.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/wireless/marvell/mwifiex/pcie.c b/drivers/net/wireless/marvell/mwifiex/pcie.c
index c6ccce426b49..641fa539de1f 100644
--- a/drivers/net/wireless/marvell/mwifiex/pcie.c
+++ b/drivers/net/wireless/marvell/mwifiex/pcie.c
@@ -1490,6 +1490,14 @@ mwifiex_pcie_send_data(struct mwifiex_adapter *adapter, struct sk_buff *skb,
 			ret = -1;
 			goto done_unmap;
 		}
+
+		/* The firmware (latest version 15.68.19.p21) of the 88W8897 PCIe+USB card
+		 * seems to crash randomly after setting the TX ring write pointer when
+		 * ASPM powersaving is enabled. A workaround seems to be keeping the bus
+		 * busy by reading a random register afterwards.
+		 */
+		mwifiex_read_reg(adapter, PCI_VENDOR_ID, &rx_val);
+
 		if ((mwifiex_pcie_txbd_not_full(card)) &&
 		    tx_param->next_pkt_len) {
 			/* have more packets and TxBD still can hold more */
-- 
2.31.1

