[PATCH] usb: cdns3: exit cdns3_gadget_udc_start if FAST_REG_ACCESS cannot be set

[Siddharth Vadapalli]

When the device is in a low power state, access to the following
registers takes a long time:
- EP_CFG
- EP_TRADDR
- EP_CMD
- EP_SEL
- EP_STS
- USB_CONF

To address this, the fast register access feature can be enabled by
setting PUSB_PWR_FST_REG_ACCESS bit of the USB_PWR register, which
allows quick access by software. Software is expected to poll on
PUSB_PWR_FST_REG_ACCESS_STAT to ensure that fast register access has
been enabled by the controller. Attempting to access any of the
aforementioned registers after setting PUSB_PWR_FST_REG_ACCESS but
before PUSB_PWR_FST_REG_ACCESS_STAT has been set will result in
undefined behavior and potentially result in system hang.

Hence, poll on PUSB_PWR_FST_REG_ACCESS_STAT before proceeding with
gadget configuration, and exit if it cannot be enabled.

Fixes: b5148d946f45 ("usb: cdns3: gadget: set fast access bit")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@xxxxxx>
---

Hello,

This patch is based on commit
92514ef226f5 Merge tag 'for-6.14-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
of Mainline Linux.

Regards,
Siddharth.

 drivers/usb/cdns3/cdns3-gadget.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c
index fd1beb10bba7..b62691944272 100644
--- a/drivers/usb/cdns3/cdns3-gadget.c
+++ b/drivers/usb/cdns3/cdns3-gadget.c
@@ -2971,8 +2971,6 @@ static void cdns3_gadget_config(struct cdns3_device *priv_dev)
 	/* enable generic interrupt*/
 	writel(USB_IEN_INIT, &regs->usb_ien);
 	writel(USB_CONF_CLK2OFFDS | USB_CONF_L1DS, &regs->usb_conf);
-	/*  keep Fast Access bit */
-	writel(PUSB_PWR_FST_REG_ACCESS, &priv_dev->regs->usb_pwr);
 
 	cdns3_configure_dmult(priv_dev, NULL);
 }
@@ -2990,6 +2988,8 @@ static int cdns3_gadget_udc_start(struct usb_gadget *gadget,
 	struct cdns3_device *priv_dev = gadget_to_cdns3_device(gadget);
 	unsigned long flags;
 	enum usb_device_speed max_speed = driver->max_speed;
+	int ret;
+	u32 reg;
 
 	spin_lock_irqsave(&priv_dev->lock, flags);
 	priv_dev->gadget_driver = driver;
@@ -2997,6 +2997,20 @@ static int cdns3_gadget_udc_start(struct usb_gadget *gadget,
 	/* limit speed if necessary */
 	max_speed = min(driver->max_speed, gadget->max_speed);
 
+	/*  keep Fast Access bit */
+	writel(PUSB_PWR_FST_REG_ACCESS, &priv_dev->regs->usb_pwr);
+	reg = readl(&priv_dev->regs->usb_pwr);
+	if (!(reg & PUSB_PWR_FST_REG_ACCESS_STAT)) {
+		ret = readl_poll_timeout_atomic(&priv_dev->regs->usb_pwr, reg,
+						(reg & PUSB_PWR_FST_REG_ACCESS_STAT),
+						10, 1000);
+		if (ret) {
+			dev_err(priv_dev->dev, "Failed to enable fast access\n");
+			spin_unlock_irqrestore(&priv_dev->lock, flags);
+			return ret;
+		}
+	}
+
 	switch (max_speed) {
 	case USB_SPEED_FULL:
 		writel(USB_CONF_SFORCE_FS, &priv_dev->regs->usb_conf);
-- 
2.43.0