[PATCH 2/3] usb: aspeed-vhub: support remote wakeup feature
neal_liu at aspeedtech.com
Thu Dec 2 14:03:27 AEDT 2021
> -----Original Message-----
> From: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Sent: Wednesday, December 1, 2021 7:38 AM
> To: Neal Liu <neal_liu at aspeedtech.com>; Felipe Balbi <balbi at kernel.org>;
> Greg Kroah-Hartman <gregkh at linuxfoundation.org>; Joel Stanley
> <joel at jms.id.au>; Andrew Jeffery <andrew at aj.id.au>; Cai Huoqing
> <caihuoqing at baidu.com>; Tao Ren <rentao.bupt at gmail.com>; Julia Lawall
> <julia.lawall at inria.fr>; kernel test robot <lkp at intel.com>; Sasha Levin
> <sashal at kernel.org>; linux-usb at vger.kernel.org; linux-kernel at vger.kernel.org;
> linux-arm-kernel at lists.infradead.org; linux-aspeed at lists.ozlabs.org
> Subject: Re: [PATCH 2/3] usb: aspeed-vhub: support remote wakeup feature
> On Tue, 2021-11-30 at 09:47 +0000, Neal Liu wrote:
> > > Should this be controlled by d->wakeup_en ? IE, we have a feature
> > > for the host to enable/disable remote wakeup, should we honor it ?
> > For KVM usage, remote keyboard packet would be sent if user wants to do
> remote wakeup.
> > In this case, d->wakeup_en is not used.
> > Set VHUB_CTRL_AUTO_REMOTE_WAKEUP to enable HW automatically
> > wakeup if any packet would be transferred.
> Sorry, I don't fully understand your explanation here.
> Normally, a USB device will do remote wakeup if it's instructed to do so via the
> appropriate feature being set, which is what wakeup_en reflects. I hadn't
> originally plumbed it in, I forgot why, I think something was either not properly
> documented or not working when I wrote that driver.
> You seem to want to override the behaviour and always send a remote wakeup
> packet no matter what. I am not sure this is desirable for all use cases, and
> might be something we want to make configurable, no ?
> I'm trying to understand your sentence, you seem to imply that the only use
> case here is "KVM" (as in remote USB on a server system) which I can probably
> agree with... mostly.
> And you say in that case, we should always do remote wakeup whenever an
> emulated USB device has any activity (keyboard or otherwise), regardless of
> whether the server has enabled the feature or not.
> Am I correct ? What's the rationale here ?
Let's me describe more details for our hardware behavior and hope you understand.
Set HUB00 implies USB device will do remote wakeup if any write command to vhub register.
Set HUB00 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 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 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.
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