linux-kernel - Re: [PATCH 2/3] usb: aspeed-vhub: support remote wakeup feature

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Message-ID: <07472b315d6adecb874f29128e9b5fe3eadad590.camel@kernel.crashing.org>
Date:   Mon, 06 Dec 2021 11:08:42 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
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-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 2/3] usb: aspeed-vhub: support remote wakeup feature

On Thu, 2021-12-02 at 03:03 +0000, Neal Liu wrote:
> > 
> Let's me describe more details for our hardware behavior and hope you
> understand.
> 
> HUB00[3]: MANUAL_REMOTE_WAKEUP
> HUB00[4]: AUTO_REMOTE_WAKEUP
> 
> Set HUB00[3] implies USB device will do remote wakeup if any write
> command to vhub register.
> Set HUB00[4] implies USB device will do remote wakeup. It can only be
> set in suspend state.
> 
> For current design, d->wakeup_en only controls whether HUB00[4] can
> be set through usb_gadget_ops.wakeup().
> If some applications (take KVM as example) want to wakeup host by
> sending a packet, it won't go through sb_gadget_ops.wakeup().
> We enable HUB00[3] to fix this problem. It won't override above
> mentioned behavior.
> If host has enabled the USB_DEVICE_REMOTE_WAKEUP feature, it has 2
> ways to wakeup host.
> 1. set srp 1 (/sys/device/platform/xxxxxxxxx/udc/xxxxxx/srp)
> 2. emulated device has activity
> If host has disabled the USB_DEVICE_REMOTE_WAKEUP feature, these 2
> ways still cannot wakeup host even if USB bus is in resume state.
> Thanks

So what you are saying is that currently, the various gadgets aren't
calling usb_gadget_wakeup() ?

Ie. it should be a gadget policy to decide when to wake-up I suppose,
but it's true that nothing in the core nor the existing gadgets seem to
handle that.

I think what you propose is a band-aid. The real problem is that the
gadget drivers should trigger wakeups (or the core should do so on
activity).

That said, for now, I don't object to adding that "auto" bit, but I
would prefer if that behaviour was use configurable.

Cheers,
Ben.