Re: [PATCH] usb: cdns3: Fix: ARM core hang after connect/disconnect operation.

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jan 08, 2020 at 12:37:18PM +0100, Pawel Laszczak wrote:
> The ARM core hang when access USB register after tens of thousands
> connect/disconnect operation.
> 
> The issue was observed on platform with android system and is not easy
> to reproduce. During test controller works at HS device mode with host
> connected.
> 
> The test is based on continuous disabling/enabling USB device function
> what cause continuous setting DEVDS/DEVEN bit in USB_CONF register.
> 
> For testing was used composite device consisting from ADP and RNDIS
> function.
> 
> Presumably the problem was caused by DMA transfer made after setting
> DEVDS bit. To resolve this issue fix stops all DMA transfer before
> setting DEVDS bit.
> 
> Signed-off-by: Pawel Laszczak <pawell@cadence.com>
> Signed-off-by: Peter Chan <peter.chan@nxp.com>
> Reported-by: Peter Chan <peter.chan@nxp.com>
> Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")

As this is in the 5.4 kernel release, you should have a "Cc: stable..."
line in here, right?

> ---
>  drivers/usb/cdns3/gadget.c | 84 ++++++++++++++++++++++++++------------
>  drivers/usb/cdns3/gadget.h |  1 +
>  2 files changed, 58 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/usb/cdns3/gadget.c b/drivers/usb/cdns3/gadget.c
> index 4c1e75509303..277ed8484032 100644
> --- a/drivers/usb/cdns3/gadget.c
> +++ b/drivers/usb/cdns3/gadget.c
> @@ -1516,6 +1516,49 @@ static int cdns3_ep_onchip_buffer_reserve(struct cdns3_device *priv_dev,
>  	return 0;
>  }
>  
> +static int cdns3_disable_reset_ep(struct cdns3_device *priv_dev,
> +				  struct cdns3_endpoint *priv_ep)
> +{
> +	unsigned long flags;
> +	u32 val;
> +	int ret;
> +
> +	spin_lock_irqsave(&priv_dev->lock, flags);
> +
> +	if (priv_ep->flags & EP_HW_RESETED) {

Is "reseted" a word?  :)

> +		spin_unlock_irqrestore(&priv_dev->lock, flags);
> +		return 0;
> +	}
> +
> +	cdns3_select_ep(priv_dev, priv_ep->endpoint.desc->bEndpointAddress);
> +
> +	val = readl(&priv_dev->regs->ep_cfg);
> +	val &= ~EP_CFG_ENABLE;
> +	writel(val, &priv_dev->regs->ep_cfg);
> +
> +	/**

No need for kernel-doc comment style please.

> +	 * Driver needs some time before resetting endpoint.
> +	 * It need waits for clearing DBUSY bit or for timeout expired.
> +	 * 10us is enough time for controller to stop transfer.
> +	 */
> +	readl_poll_timeout_atomic(&priv_dev->regs->ep_sts, val,
> +				  !(val & EP_STS_DBUSY), 1, 10);

You don't care if you time out?

> +	writel(EP_CMD_EPRST, &priv_dev->regs->ep_cmd);
> +
> +	ret = readl_poll_timeout_atomic(&priv_dev->regs->ep_cmd, val,
> +					!(val & (EP_CMD_CSTALL | EP_CMD_EPRST)),
> +					1, 1000);
> +
> +	if (unlikely(ret))

Unless you can measure the difference of using/not using a
unlikely/likely mark, NEVER use it.  The compiler and cpu can almost
always do better than you can, we have the tests to prove it.

> +		dev_err(priv_dev->dev, "Timeout: %s resetting failed.\n",
> +			priv_ep->name);
> +
> +	priv_ep->flags |= EP_HW_RESETED;

So an error happens, but you still claim the device is reset?  What can
a user do about this error?

Yes, I know you copied this from other code in this driver, but it
doesn't look right to me.

> +	spin_unlock_irqrestore(&priv_dev->lock, flags);

Why print while a spinlock is held?  That's mean, you could have printed
here, right?

> +
> +	return ret;
> +}
> +
>  void cdns3_configure_dmult(struct cdns3_device *priv_dev,
>  			   struct cdns3_endpoint *priv_ep)
>  {
> @@ -1893,8 +1936,6 @@ static int cdns3_gadget_ep_disable(struct usb_ep *ep)
>  	struct usb_request *request;
>  	unsigned long flags;
>  	int ret = 0;
> -	u32 ep_cfg;
> -	int val;
>  
>  	if (!ep) {
>  		pr_err("usbss: invalid parameters\n");
> @@ -1908,32 +1949,11 @@ static int cdns3_gadget_ep_disable(struct usb_ep *ep)
>  			  "%s is already disabled\n", priv_ep->name))
>  		return 0;
>  
> -	spin_lock_irqsave(&priv_dev->lock, flags);
> -
>  	trace_cdns3_gadget_ep_disable(priv_ep);
>  
> -	cdns3_select_ep(priv_dev, ep->desc->bEndpointAddress);
> -
> -	ep_cfg = readl(&priv_dev->regs->ep_cfg);
> -	ep_cfg &= ~EP_CFG_ENABLE;
> -	writel(ep_cfg, &priv_dev->regs->ep_cfg);
> -
> -	/**
> -	 * Driver needs some time before resetting endpoint.
> -	 * It need waits for clearing DBUSY bit or for timeout expired.
> -	 * 10us is enough time for controller to stop transfer.
> -	 */
> -	readl_poll_timeout_atomic(&priv_dev->regs->ep_sts, val,
> -				  !(val & EP_STS_DBUSY), 1, 10);
> -	writel(EP_CMD_EPRST, &priv_dev->regs->ep_cmd);
> -
> -	readl_poll_timeout_atomic(&priv_dev->regs->ep_cmd, val,
> -				  !(val & (EP_CMD_CSTALL | EP_CMD_EPRST)),
> -				  1, 1000);
> -	if (unlikely(ret))
> -		dev_err(priv_dev->dev, "Timeout: %s resetting failed.\n",
> -			priv_ep->name);
> +	cdns3_disable_reset_ep(priv_dev, priv_ep);
>  
> +	spin_lock_irqsave(&priv_dev->lock, flags);
>  	while (!list_empty(&priv_ep->pending_req_list)) {
>  		request = cdns3_next_request(&priv_ep->pending_req_list);
>  
> @@ -1962,6 +1982,7 @@ static int cdns3_gadget_ep_disable(struct usb_ep *ep)
>  
>  	ep->desc = NULL;
>  	priv_ep->flags &= ~EP_ENABLED;
> +	priv_ep->flags |= EP_CLAIMED | EP_HW_RESETED;

Why do you now set EP_CLAIMED here when you never set that before?  Is
this a different type of change?

thanks,

greg k-h