linux-kernel - [PATCH v2] usb: dwc3: core: Do not perform GCTL_CORE

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Message-ID: <20220714045625.20377-1-quic_rkollals@quicinc.com>
Date:   Thu, 14 Jul 2022 10:26:25 +0530
From:   Rohith Kollalsi <quic_rkollals@...cinc.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Rohith Kollalsi" <quic_rkollals@...cinc.com>
Subject: [PATCH v2] usb: dwc3: core: Do not perform GCTL_CORE_SOFTRESET during bootup

According to the programming guide, it is recommended to
perform a GCTL_CORE_SOFTRESET only when switching the mode
from device to host or host to device. However, it is found
that during bootup when __dwc3_set_mode() is called for the
first time, GCTL_CORESOFTRESET is done with suspendable bit(BIT 17)
of DWC3_GUSB3PIPECTL set. This some times leads to issues
like controller going into bad state and controller registers
reading value zero. Until GCTL_CORESOFTRESET is done and
run/stop bit is set core initialization is not complete.
Setting suspendable bit of DWC3_GUSB3PIPECTL and then
performing GCTL_CORESOFTRESET is therefore not recommended.
Avoid this by only performing the reset if current_dr_role is set,
that is, when doing subsequent role switching.

Fixes: f88359e1588b ("usb: dwc3: core: Do core softreset when switch mode")
Signed-off-by: Rohith Kollalsi <quic_rkollals@...cinc.com>
---
v2: Explaining the scenario in a better way in the comment before
    GCTL.CoreSoftReset.

 drivers/usb/dwc3/core.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 050b2ba5986d..c5c238ab3083 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -158,9 +158,13 @@ static void __dwc3_set_mode(struct work_struct *work)
 		break;
 	}

-	/* For DRD host or device mode only */
-	if ((DWC3_IP_IS(DWC3) || DWC3_VER_IS_PRIOR(DWC31, 190A)) &&
-	    dwc->desired_dr_role != DWC3_GCTL_PRTCAP_OTG) {
+	/*
+	 * When current_dr_role is not set, there's no role switching.
+	 * Only perform GCTL.CoreSoftReset when there's DRD role switching.
+	 */
+	if (dwc->current_dr_role && ((DWC3_IP_IS(DWC3) ||
+			DWC3_VER_IS_PRIOR(DWC31, 190A)) &&
+			dwc->desired_dr_role != DWC3_GCTL_PRTCAP_OTG)) {
 		reg = dwc3_readl(dwc->regs, DWC3_GCTL);
 		reg |= DWC3_GCTL_CORESOFTRESET;
 		dwc3_writel(dwc->regs, DWC3_GCTL, reg);
-- 
2.17.1