linux-kernel - Re: [PATCH] usb: xhci: skip re-check pending port event if hibernated

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Message-ID: <609eb0eea02b2304f427d4f2e9c26de9f2149f06.camel@mediatek.com>
Date:   Fri, 17 Dec 2021 17:40:15 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Jun Li <lijun.kernel@...il.com>
CC:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Eddie Hung <eddie.hung@...iatek.com>,
        Yun-Chien Yu <yun-chien.yu@...iatek.com>
Subject: Re: [PATCH] usb: xhci: skip re-check pending port event if
 hibernated

On Tue, 2021-12-14 at 12:05 +0200, Mathias Nyman wrote:
> On 14.12.2021 10.00, Jun Li wrote:
> > Mathias Nyman <mathias.nyman@...ux.intel.com> 于2021年12月11日周六
> > 01:56写道：
> > > 
> > > On 9.12.2021 9.22, Chunfeng Yun wrote:
> > > > When xHCI controller hibernated, the root hub lost power, if
> > > > controller
> > > > support Port Power Control (PPC), PP is not set at
> > > > xhci_resume() and
> > > > set by hub_reset_resume() later, so no need check pending port
> > > > event.
> > > > If PPC is not supported, device is disconneced, seems do not
> > > > send out
> > > > U3 LFPS wake signal, no need re-check again and drop 120ms
> > > > delay to
> > > > save resume time.
> > > > 
> > > > Reported-by: Yun-Chien Yu <yun-chien.yu@...iatek.com>
> > > > Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> > > > ---
> > > 
> > > Thanks, adding
> > 
> > Hi Mathias, Chunfeng
> > 
> > I have a question on this, if there is no any usb devices connected
> > before suspend, do we need this 120ms delay to check again?
> > So do we need one more condition to limit this like?
> > if (!pending_portevent && !hibernated && xhci_has_child_device())
> 
> The 120ms delay was added to make sure we catch the second wake
> signal
> from a device in case host missed the first U3 exit LFPS wakeup
> signal.
> 
> Even if no devices are connected this might be helpful if a device is
> connected while host is suspended.
> I haven't checked any timing for the link training during
> enumeration,
> but it also uses LFPS signalling, and connected device isn't visible
> to
> driver until link is successfully trained.
For xhci-mtk, roothub can't detect device until root hub set PortPower,
seems also the same for other xhci controllers that support Port Power
Control.
> 
> So the original 120ms delay patch might as a positive side effect
> ensure
> driver doesn't suspend host mid device enumeration.
this is in resume?

> 
> Could be looked into more, but I don't think we should this patch by
> Chunfeng
> 
> Thanks
> Mathias