[PATCH] usb: cdns3: use VBUS Valid to determine role for dr_mode OTG

[Siddharth Vadapalli]

The cdns3_bind() function is responsible for identifying the appropriate
driver to bind to the USB Controller's device-tree node. If the device-tree
node has the 'dr_mode' property set to 'otg', the existing approach fails
to bind a driver, leading to loss of functionality.

To address this, use the VBUS Valid field of the OTG Status register to
determine the role as follows:
- If VBUS Valid field is set, it indicates that a USB Host is supplying
  power and the Controller should assume the Peripheral role.
- If VBUS Valid field is clear, it indicates the absence of a USB Host and
  the Controller should assume the Host role.

Additionally, when 'dr_mode' happens to be 'otg' and the STRAP settings
are not specified, use VBUS Valid to determine the role in cdns3_drd_init()
and assign it to cdns->dr_mode.

Signed-off-by: Siddharth Vadapalli <s-vadapalli at ti.com>
---

Hello,

This patch is based on commit
a8d982e1f17 x86: cpu: Fix crash on FTRACE enabled builds
of the master branch of U-Boot.

Patch has been tested in the context of USB DFU boot on the J784S4 SoC
with a Cadence USB 3.0 Controller. Since the Linux device-tree for the
J784S4-EVM specifies the 'dr_mode' as OTG, due to reuse of Linux
device-tree by U-Boot, the 'dr_mode' of 'otg' causes USB DFU Boot to fail.
While one approach to fix it is to update 'dr_mode' to 'peripheral' in
the 'k3-j784s4-u-boot.dtsi' file as a HACK, it doesn't scale to other
SoCs and all of their 'u-boot.dtsi' files will have to be udpated as well.
While I am providing Texas Instruments SoCs as an example, I presume that
SoCs from other vendors are also affected by the 'dr_mode' being 'otg'.
This patch addresses the issue by using the VBUS Valid bit of the OTG
status register to override 'dr_mode' from 'otg' to a deterministic role
to enable functionality.

The USB DFU Boot Logs for the R5 SPL stage on J784S4 SoC with the current
U-Boot master as of commit
a8d982e1f17 x86: cpu: Fix crash on FTRACE enabled builds
are:
https://gist.github.com/Siddharth-Vadapalli-at-TI/b910f326b6c9fad760190bd299ae3ff3
and the logs indicate that USB DFU Boot fails. The failure is specifically
due to 'dr_mode' being 'otg' and the cdns3_bind() function failing to bind
the device-tree node to the peripheral driver required for DFU Boot.

The USB DFU Boot Logs for the R5 SPL stage with just this patch applied
while leaving 'dr_mode' at its existing value of 'otg' are:
https://gist.github.com/Siddharth-Vadapalli-at-TI/033b9772b6ab105b96806adf890848fe

Regards,
Siddharth.

 drivers/usb/cdns3/core.c | 53 ++++++++++++++++++++++++++++++++++++++++
 drivers/usb/cdns3/drd.c  | 11 +++++++++
 2 files changed, 64 insertions(+)

diff --git a/drivers/usb/cdns3/core.c b/drivers/usb/cdns3/core.c
index 4434dc15bec..b7be5c48fc9 100644
--- a/drivers/usb/cdns3/core.c
+++ b/drivers/usb/cdns3/core.c
@@ -392,6 +392,55 @@ static const struct udevice_id cdns3_ids[] = {
 	{ },
 };
 
+/*
+ * The VBUS Valid Bit in the OTG Status register can be used to determine
+ * the role. When VBUS Valid is set, it indicates that a USB Host is supplying
+ * power, so the Controller should assume the PERIPHERAL role. If it isn't set,
+ * it indicates the absence of a USB Host, so the Controller should assume the
+ * HOST role. If the OTG Status register is inaccessible, return OTG role.
+ */
+static enum usb_dr_mode cdns3_get_otg_mode(ofnode node)
+{
+	struct cdns3 cdns, *cdnsp;
+	void __iomem *otg_regs;
+	fdt_addr_t otg_addr;
+	int otg_reg_index;
+	int vbus;
+
+	otg_reg_index = ofnode_stringlist_search(node, "reg-names", "otg");
+	if (otg_reg_index < 0)
+		return USB_DR_MODE_OTG;
+
+	otg_addr = ofnode_get_addr_index(node, otg_reg_index);
+	if (otg_addr == FDT_ADDR_T_NONE)
+		return USB_DR_MODE_OTG;
+
+	otg_regs = map_physmem(otg_addr, 0, MAP_NOCACHE);
+	if (!otg_regs)
+		return USB_DR_MODE_OTG;
+
+	/*
+	 * As mentioned in drivers/usb/cdns3/drd.c, there are two versions
+	 * of the Controller. The following logic detects the version of the
+	 * Controller and interprets the register layout accordingly.
+	 */
+	cdnsp = &cdns;
+	cdnsp->otg_v0_regs = otg_regs;
+	if (!readl(&cdnsp->otg_v0_regs->cmd)) {
+		cdnsp->otg_regs = otg_regs;
+	} else {
+		cdnsp->otg_v1_regs = otg_regs;
+		cdnsp->otg_regs = (void *)&cdnsp->otg_v1_regs->cmd;
+	}
+
+	/* Use VBUS Valid to determine role */
+	vbus = !!(readl(&cdnsp->otg_regs->sts) & OTGSTS_VBUS_VALID);
+	if (vbus)
+		return USB_DR_MODE_PERIPHERAL;
+	else
+		return USB_DR_MODE_HOST;
+}
+
 int cdns3_bind(struct udevice *parent)
 {
 	enum usb_dr_mode dr_mode;
@@ -413,6 +462,10 @@ int cdns3_bind(struct udevice *parent)
 	if (dr_mode == USB_DR_MODE_UNKNOWN)
 		dr_mode = usb_get_dr_mode(dev_ofnode(parent));
 
+	/* Use VBUS Valid to determine role */
+	if (dr_mode == USB_DR_MODE_OTG)
+		dr_mode = cdns3_get_otg_mode(node);
+
 	switch (dr_mode) {
 #if defined(CONFIG_SPL_USB_HOST) || \
 	(!defined(CONFIG_XPL_BUILD) && defined(CONFIG_USB_HOST))
diff --git a/drivers/usb/cdns3/drd.c b/drivers/usb/cdns3/drd.c
index cbb13342343..0ca40a5cc8d 100644
--- a/drivers/usb/cdns3/drd.c
+++ b/drivers/usb/cdns3/drd.c
@@ -301,6 +301,17 @@ int cdns3_drd_init(struct cdns3 *cdns)
 		cdns->dr_mode = USB_DR_MODE_PERIPHERAL;
 	}
 
+	/*
+	 * In the absence of STRAP configuration, use VBUS Valid to
+	 * determine the appropriate role to be assigned to dr_mode.
+	 */
+	if (cdns->dr_mode == USB_DR_MODE_OTG) {
+		if (cdns3_get_vbus(cdns))
+			cdns->dr_mode = USB_DR_MODE_PERIPHERAL;
+		else
+			cdns->dr_mode = USB_DR_MODE_HOST;
+	}
+
 	state = readl(&cdns->otg_regs->sts);
 	if (OTGSTS_OTG_NRDY(state) != 0) {
 		dev_err(cdns->dev, "Cadence USB3 OTG device not ready\n");
-- 
2.51.1