On Wed, Aug 28, 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@xxxxxxxxxxxxxxx>
> Suggested-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
> Signed-off-by: Prashanth K <quic_prashk@xxxxxxxxxxx>
> ---
> v5: Further rewording of the comment in function.
> v4: Rewording the comment in function definition.
> v3: Added notes on top the function definition.
> v2: Refactored the patch as suggested in v1 discussion.
>
> drivers/usb/dwc3/gadget.c | 41 ++++++++++++++++-----------------------
> 1 file changed, 17 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 89fc690fdf34..291bc549935b 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -287,6 +287,23 @@ static int __dwc3_gadget_wakeup(struct dwc3 *dwc, bool async);
> *
> * Caller should handle locking. This function will issue @cmd with given
> * @params to @dep and wait for its completion.
> + *
> + * According to the programming guide, if the link state is in L1/L2/U3,
> + * then sending the Start Transfer command may not complete. The
> + * programming guide suggested to bring the link state back to ON/U0 by
> + * performing remote wakeup prior to sending the command. However, don't
> + * initiate remote wakeup when the user/function does not send wakeup
> + * request via wakeup ops. Send the command when it's allowed.
> + *
> + * Notes:
> + * For L1 link state, issuing a command requires the clearing of
> + * GUSB2PHYCFG.SUSPENDUSB2, which turns on the signal required to complete
> + * the given command (usually within 50us). This should happen within the
> + * command timeout set by driver. No additional step is needed.
> + *
> + * For L2 or U3 link state, the gadget is in USB suspend. Care should be
> + * taken when sending Start Transfer command to ensure that it's done after
> + * USB resume.
> */
> int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
> struct dwc3_gadget_ep_cmd_params *params)
> @@ -327,30 +344,6 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
> dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);
> }
>
> - 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
>
Acked-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
Thanks,
Thinh
