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

On 25-02-07 11:12:50, Siddharth Vadapalli wrote:

On Fri, Feb 07, 2025 at 10:25:23AM +0800, Peter Chen wrote:

Hello Peter,

...

On 25-02-06 18:29:36, Siddharth Vadapalli wrote:

...

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@vger.kernel.org Signed-off-by: Siddharth Vadapalli s-vadapalli@ti.com

---

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);

Hi Siddharth,

Would you please keep this change at cdns3_gadget_config in case the controller is power lost during the system suspend?

I did think of that initially, but the problem with doing so is that we are already accessing USB_CONF above in the "switch(max_speed)" section. The PUSB_PWR_FST_REG_ACCESS bit needs to be set before accessing any of:

• EP_CFG
• EP_TRADDR
• EP_CMD
• EP_SEL
• EP_STS
• USB_CONF

Please let me know if you have an alternate suggestion to address the above.

How about move cdns3_gadget_config at the beginning of function cdns3_gadget_udc_start, and add your changes at cdns3_gadget_config?

Regards, Peter