linux-kernel - [RFC] usb: dwc3: core: set force_gen1 bit in USB31 devices if max speed is SS

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Date:   Fri, 12 May 2023 22:31:07 +0530
From:   Krishna Kurapati <quic_kriskura@...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>,
        <quic_ppratap@...cinc.com>, <quic_wcheng@...cinc.com>,
        <quic_jackp@...cinc.com>,
        Krishna Kurapati <quic_kriskura@...cinc.com>
Subject: [RFC] usb: dwc3: core: set force_gen1 bit in USB31 devices if max speed is SS

Currently for dwc3_usb31 devices, if maximum_speed is limited to
super-speed in DT, then device mode is limited to SS, but host mode
still works in SSP.

The documentation for max-speed property is as follows:

"Tells USB controllers we want to work up to a certain speed.
Incase  this isn't passed via DT, USB controllers should default to
their maximum HW capability."

It doesn't specify that the property is only for device mode.
Fix this by forcing controller supported max speed to Gen1 by
setting LLUCTL.Force_Gen1 bit if controller is DWC3_USB31 and
max speed is mentioned as SS in DT.

Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
---
Discussion regarding the same at:
https://lore.kernel.org/all/e465c69c-3a9d-cbdb-d44e-96b99cfa1a92@quicinc.com/

 drivers/usb/dwc3/core.c | 13 +++++++++++++
 drivers/usb/dwc3/core.h |  4 ++++
 2 files changed, 17 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 0beaab932e7d..989dc76ecbca 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -116,6 +116,18 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode)
 	dwc->current_dr_role = mode;
 }
 
+static void dwc3_configure_host_speed(struct dwc3 *dwc)
+{
+	u32 reg;
+
+	if (DWC3_IP_IS(DWC31) &&
+	   (dwc->maximum_speed == USB_SPEED_SUPER)) {
+		reg = dwc3_readl(dwc->regs, DWC3_LLUCTL);
+		reg |= DWC3_LLUCTL_FORCE_GEN1;
+		dwc3_writel(dwc->regs, DWC3_LLUCTL, reg);
+	}
+}
+
 static void __dwc3_set_mode(struct work_struct *work)
 {
 	struct dwc3 *dwc = work_to_dwc(work);
@@ -194,6 +206,7 @@ static void __dwc3_set_mode(struct work_struct *work)
 
 	switch (desired_dr_role) {
 	case DWC3_GCTL_PRTCAP_HOST:
+		dwc3_configure_host_speed(dwc);
 		ret = dwc3_host_init(dwc);
 		if (ret) {
 			dev_err(dwc->dev, "failed to initialize host\n");
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index d56457c02996..29b780a58dc6 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -121,6 +121,10 @@
 #define DWC3_GPRTBIMAP_FS0	0xc188
 #define DWC3_GPRTBIMAP_FS1	0xc18c
 #define DWC3_GUCTL2		0xc19c
+#define DWC3_LLUCTL		0xd024
+
+/* Force Gen1 speed on Gen2 link */
+#define DWC3_LLUCTL_FORCE_GEN1	BIT(10)
 
 #define DWC3_VER_NUMBER		0xc1a0
 #define DWC3_VER_TYPE		0xc1a4
-- 
2.40.0