linux-kernel - RE: [PATCH v3 2/4] usb: aspeed-vhub: fix remote wakeup failure in iKVM use case

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Date:   Mon, 20 Dec 2021 02:22:50 +0000
From:   Neal Liu <neal_liu@...eedtech.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Cai Huoqing <caihuoqing@...du.com>,
        Tao Ren <rentao.bupt@...il.com>,
        Julia Lawall <julia.lawall@...ia.fr>,
        kernel test robot <lkp@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>
CC:     BMC-SW <BMC-SW@...eedtech.com>
Subject: RE: [PATCH v3 2/4] usb: aspeed-vhub: fix remote wakeup failure in
 iKVM use case

> -----Original Message-----
> From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Sent: Tuesday, December 14, 2021 10:36 AM
> To: Neal Liu <neal_liu@...eedtech.com>; Felipe Balbi <balbi@...nel.org>;
> Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Joel Stanley
> <joel@....id.au>; Andrew Jeffery <andrew@...id.au>; Cai Huoqing
> <caihuoqing@...du.com>; Tao Ren <rentao.bupt@...il.com>; Julia Lawall
> <julia.lawall@...ia.fr>; kernel test robot <lkp@...el.com>; Sasha Levin
> <sashal@...nel.org>; linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; linux-aspeed@...ts.ozlabs.org
> Cc: BMC-SW <BMC-SW@...eedtech.com>
> Subject: Re: [PATCH v3 2/4] usb: aspeed-vhub: fix remote wakeup failure in
> iKVM use case
> 
> On Thu, 2021-12-09 at 02:37 +0000, Neal Liu wrote:
> > I'm confused. Signaling Wakeup when wakeup_en is set if it has any ep
> > activities is not exactly what you said?
> >
> > wakeup_en is set only if host allows this device have wakeup
> > capability and bus being suspended.
> >
> > Normal ep activities would not write the MMIO because wakeup_en is not
> > set.
> 
> Hrm... I didn't think wakeup_en was limited to the bus being suspended, but
> maybe I misremember, it's been a while.
> 
> Cheers,
> Ben.
> 

wakeup_en is only set in the case of host set USB_DEVICE_REMOTE_WAKEUP feature to vhub devices.
I think this behavior only occurs during host is going to suspend, and set this feature to any device which can wakeup itself before sleep.
Thanks

-Neal