linux-kernel - [PATCH] usb: cdns3: fix race condition before setting doorbell

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Date:   Tue, 7 Sep 2021 08:26:19 +0200
From:   Pawel Laszczak <pawell@...ence.com>
To:     <peter.chen@...nel.org>
CC:     <pawell@...ence.com>, <rogerq@...nel.org>, <a-govindraju@...com>,
        <gregkh@...uxfoundation.org>, <felipe.balbi@...ux.intel.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: [PATCH] usb: cdns3: fix race condition before setting doorbell

From: Pawel Laszczak <pawell@...ence.com>

For DEV_VER_V3 version there exist race condition between clearing
ep_sts.EP_STS_TRBERR and setting ep_cmd.EP_CMD_DRDY bit.
Setting EP_CMD_DRDY will be ignored by controller when
EP_STS_TRBERR is set. So, between these two instructions we have
a small time gap in which the EP_STSS_TRBERR can be set. In such case
the transfer will not start after setting doorbell.

Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
cc: <stable@...r.kernel.org> # 5.12.x
Signed-off-by: Pawel Laszczak <pawell@...ence.com>
---
 drivers/usb/cdns3/cdns3-gadget.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c
index 80aaab159e58..e9769fab21ea 100644
--- a/drivers/usb/cdns3/cdns3-gadget.c
+++ b/drivers/usb/cdns3/cdns3-gadget.c
@@ -1100,6 +1100,19 @@ static int cdns3_ep_run_stream_transfer(struct cdns3_endpoint *priv_ep,
 	return 0;
 }
 
+static void cdns3_rearm_drdy_if_needed(struct cdns3_endpoint *priv_ep)
+{
+	struct cdns3_device *priv_dev = priv_ep->cdns3_dev;
+
+	if (priv_dev->dev_ver < DEV_VER_V3)
+		return;
+
+	if (readl(&priv_dev->regs->ep_sts) & EP_STS_TRBERR) {
+		writel(EP_STS_TRBERR, &priv_dev->regs->ep_sts);
+		writel(EP_CMD_DRDY, &priv_dev->regs->ep_cmd);
+	}
+}
+
 /**
  * cdns3_ep_run_transfer - start transfer on no-default endpoint hardware
  * @priv_ep: endpoint object
@@ -1351,6 +1364,7 @@ static int cdns3_ep_run_transfer(struct cdns3_endpoint *priv_ep,
 		/*clearing TRBERR and EP_STS_DESCMIS before seting DRDY*/
 		writel(EP_STS_TRBERR | EP_STS_DESCMIS, &priv_dev->regs->ep_sts);
 		writel(EP_CMD_DRDY, &priv_dev->regs->ep_cmd);
+		cdns3_rearm_drdy_if_needed(priv_ep);
 		trace_cdns3_doorbell_epx(priv_ep->name,
 					 readl(&priv_dev->regs->ep_traddr));
 	}
-- 
2.25.1