linux-kernel - Re: [PATCH v1 3/3] usb: dwc3: gadget: Make gadget

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Message-ID: <20250409004330.iflfdxabodalsmox@synopsys.com>
Date: Wed, 9 Apr 2025 00:43:33 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Prashanth K <prashanth.k@....qualcomm.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Bakker <kees@...erbout.nl>,
        William McVicker <willmcvicker@...gle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...nel.org" <stable@...nel.org>
Subject: Re: [PATCH v1 3/3] usb: dwc3: gadget: Make gadget_wakeup asynchronous

On Tue, Apr 08, 2025, Prashanth K wrote:
> 
> 
> On 08-04-25 05:08 am, Thinh Nguyen wrote:
> > On Thu, Apr 03, 2025, Prashanth K wrote:

> >> @@ -4398,6 +4371,21 @@ static void dwc3_gadget_linksts_change_interrupt(struct dwc3 *dwc,
> >>  	}
> >>  
> >>  	dwc->link_state = next;
> >> +
> >> +	/* Proceed with func wakeup if any interfaces that has requested */
> >> +	while (dwc->func_wakeup_pending && (next == DWC3_LINK_STATE_U0)) {
> >> +		if (dwc->func_wakeup_pending & BIT(0)) {
> >> +			ret = dwc3_send_gadget_generic_command(dwc, DWC3_DGCMD_DEV_NOTIFICATION,
> >> +							       DWC3_DGCMDPAR_DN_FUNC_WAKE |
> >> +							       DWC3_DGCMDPAR_INTF_SEL(intf_id));
> >> +			if (ret)
> >> +				dev_err(dwc->dev, "function remote wakeup failed for %d, ret:%d\n",
> >> +					intf_id, ret);
> >> +		}
> >> +		dwc->func_wakeup_pending >>= 1;
> > 
> > This would break the bitmap of dwc->func_wakeup_pending. Perhaps we can
> > use ffs(x) to properly find and clear the interface ID from the bitmap
> > one at a time.
> > 
> Yes, we can use ffs(x). But I didn't understand how this would break
> bitmap of dwc->func_wakeup_pending.
> 

Since you're sending device notification to all the wakeup armed
interfaces and not reusing the func_wakeup_pending afterward, the result
of what you're doing here will be the same.

IMHO, for clarity, what I was suggesting is to revise the logic to
preserve the dwc->func_wakeup_pending bitmap instead of shifting and
overwriting it, causing the bitmap to no longer match the intf_id. We
get the intf_id from the bitmap and clear the intf_id bit from the
bitmap as we go.

Thanks,
Thinh