[v2] usb: dwc3: Avoid waking up gadget during startxfer

When operating in High-Speed, it is observed that DSTS[USBLNKST] doesn't
update link state immediately after receiving the wakeup interrupt. Since
wakeup event handler calls the resume callbacks, there is a chance that
function drivers can perform an ep queue, which in turn tries to perform
remote wakeup from send_gadget_ep_cmd(STARTXFER). This happens because
DSTS[[21:18] wasn't updated to U0 yet, it's observed that the latency of
DSTS can be in order of milli-seconds. Hence avoid calling gadget_wakeup
during startxfer to prevent unnecessarily issuing remote wakeup to host.

Fixes: c36d8e947a56 ("usb: dwc3: gadget: put link to U0 before Start Transfer")
Cc: <stable@vger.kernel.org>
Suggested-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
---
v2:  Refactored the patch as suggested in v1 discussion.

 drivers/usb/dwc3/gadget.c | 24 ------------------------
 1 file changed, 24 deletions(-)

On Fri, Aug 16, 2024, Prashanth K wrote:
> When operating in High-Speed, it is observed that DSTS[USBLNKST] doesn't
> update link state immediately after receiving the wakeup interrupt. Since
> wakeup event handler calls the resume callbacks, there is a chance that
> function drivers can perform an ep queue, which in turn tries to perform
> remote wakeup from send_gadget_ep_cmd(STARTXFER). This happens because
> DSTS[[21:18] wasn't updated to U0 yet, it's observed that the latency of
> DSTS can be in order of milli-seconds. Hence avoid calling gadget_wakeup
> during startxfer to prevent unnecessarily issuing remote wakeup to host.
> 
> Fixes: c36d8e947a56 ("usb: dwc3: gadget: put link to U0 before Start Transfer")
> Cc: <stable@vger.kernel.org>
> Suggested-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
> ---
> v2:  Refactored the patch as suggested in v1 discussion.
> 
>  drivers/usb/dwc3/gadget.c | 24 ------------------------
>  1 file changed, 24 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 89fc690fdf34..3f634209c5b8 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -327,30 +327,6 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
>  			dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);

Can you capture the notes I provided explaining why we can issue Start
Transfer without checking for L1/L2/U3 states on top of this function?

Thanks,
Thinh

>  	}
>  
> -	if (DWC3_DEPCMD_CMD(cmd) == DWC3_DEPCMD_STARTTRANSFER) {
> -		int link_state;
> -
> -		/*
> -		 * Initiate remote wakeup if the link state is in U3 when
> -		 * operating in SS/SSP or L1/L2 when operating in HS/FS. If the
> -		 * link state is in U1/U2, no remote wakeup is needed. The Start
> -		 * Transfer command will initiate the link recovery.
> -		 */
> -		link_state = dwc3_gadget_get_link_state(dwc);
> -		switch (link_state) {
> -		case DWC3_LINK_STATE_U2:
> -			if (dwc->gadget->speed >= USB_SPEED_SUPER)
> -				break;
> -
> -			fallthrough;
> -		case DWC3_LINK_STATE_U3:
> -			ret = __dwc3_gadget_wakeup(dwc, false);
> -			dev_WARN_ONCE(dwc->dev, ret, "wakeup failed --> %d\n",
> -					ret);
> -			break;
> -		}
> -	}
> -
>  	/*
>  	 * For some commands such as Update Transfer command, DEPCMDPARn
>  	 * registers are reserved. Since the driver often sends Update Transfer
> -- 
> 2.25.1
>

On 17-08-24 03:19 am, Thinh Nguyen wrote:
> On Fri, Aug 16, 2024, Prashanth K wrote:
>> When operating in High-Speed, it is observed that DSTS[USBLNKST] doesn't
>> update link state immediately after receiving the wakeup interrupt. Since
>> wakeup event handler calls the resume callbacks, there is a chance that
>> function drivers can perform an ep queue, which in turn tries to perform
>> remote wakeup from send_gadget_ep_cmd(STARTXFER). This happens because
>> DSTS[[21:18] wasn't updated to U0 yet, it's observed that the latency of
>> DSTS can be in order of milli-seconds. Hence avoid calling gadget_wakeup
>> during startxfer to prevent unnecessarily issuing remote wakeup to host.
>>
>> Fixes: c36d8e947a56 ("usb: dwc3: gadget: put link to U0 before Start Transfer")
>> Cc: <stable@vger.kernel.org>
>> Suggested-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
>> Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
>> ---
>> v2:  Refactored the patch as suggested in v1 discussion.
>>
>>  drivers/usb/dwc3/gadget.c | 24 ------------------------
>>  1 file changed, 24 deletions(-)
>>
>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>> index 89fc690fdf34..3f634209c5b8 100644
>> --- a/drivers/usb/dwc3/gadget.c
>> +++ b/drivers/usb/dwc3/gadget.c
>> @@ -327,30 +327,6 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
>>  			dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);
> 
> Can you capture the notes I provided explaining why we can issue Start
> Transfer without checking for L1/L2/U3 states on top of this function?
> 
I also thought the same initially, but didnt add since Greg usually adds
the patch link to commit, so that the discussion would be captured in
git log. I will add it on top of dwc3_send_gadget_ep_cmd and send V3,
let me know if there's any other suggestion.

Thanks,
Prashanth K