linux-kernel - [PATCH] usb: dwc3: core: Disable USB2 retry for DWC

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Message-ID: <20241129173422.20063-1-quic_faisalh@quicinc.com>
Date: Fri, 29 Nov 2024 23:04:22 +0530
From: Faisal Hassan <quic_faisalh@...cinc.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>
CC: <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Faisal Hassan
	<quic_faisalh@...cinc.com>
Subject: [PATCH] usb: dwc3: core: Disable USB2 retry for DWC_usb31 1.80a and prior

STAR 9001346572 addresses a USB 2.0 endpoint blocking issue in host mode
for controller versions DWC_usb31 1.70a and 1.80a. This issue affects
devices on both high-speed and full-speed bus instances. When all
endpoint caches are filled and a single active endpoint receives
continuous NAK responses, data transfers to other endpoints may get
blocked.

To resolve this, for controller versions DWC_usb31 1.70a and 1.80a, the
GUCTL3 bit[16] (USB2.0 Internal Retry Disable) is set to 1. This bit
disables the USB2.0 internal retry feature and ensures proper eviction
handling in the host controller endpoind cache. The GUCTL3[16] register
function is available only from DWC_usb31 version 1.70a.

Signed-off-by: Faisal Hassan <quic_faisalh@...cinc.com>
---
 drivers/usb/dwc3/core.c | 20 ++++++++++++++++++++
 drivers/usb/dwc3/core.h |  1 +
 2 files changed, 21 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 98114c2827c0..c5c36134ddd9 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -1475,6 +1475,26 @@ static int dwc3_core_init(struct dwc3 *dwc)
 		dwc3_writel(dwc->regs, DWC3_LLUCTL, reg);
 	}
 
+	/*
+	 * STAR 9001346572: This issue affects DWC_usb31 versions 1.80a and
+	 * prior. When an active endpoint not currently cached in the host
+	 * controller is chosen to be cached to the same index as an endpoint
+	 * receiving NAKs, the endpoint receiving NAKs enters continuous
+	 * retry mode. This prevents it from being evicted from the host
+	 * controller cache, blocking the new endpoint from being cached and
+	 * serviced.
+	 *
+	 * To resolve this, for controller versions 1.70a and 1.80a, set the
+	 * GUCTL3 bit[16] (USB2.0 Internal Retry Disable) to 1. This bit
+	 * disables the USB2.0 internal retry feature. The GUCTL3[16] register
+	 * function is available only from version 1.70a.
+	 */
+	if (DWC3_VER_IS_WITHIN(DWC31, 170A, 180A)) {
+		reg = dwc3_readl(dwc->regs, DWC3_GUCTL3);
+		reg |= DWC3_GUCTL3_USB20_RETRY_DISABLE;
+		dwc3_writel(dwc->regs, DWC3_GUCTL3, reg);
+	}
+
 	return 0;
 
 err_power_off_phy:
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index eab81dfdcc35..5417058c5943 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -425,6 +425,7 @@
 
 /* Global User Control Register 3 */
 #define DWC3_GUCTL3_SPLITDISABLE		BIT(14)
+#define DWC3_GUCTL3_USB20_RETRY_DISABLE		BIT(16)
 
 /* Device Configuration Register */
 #define DWC3_DCFG_NUMLANES(n)	(((n) & 0x3) << 30) /* DWC_usb32 only */
-- 
2.17.1