linux-kernel - Re: [PATCH] usb: core: Set port link to RxDetect if port is not enabled after resume

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Message-Id: <C747DCA1-B5B4-4AFC-B83C-791B3B860621@canonical.com>
Date:   Fri, 6 Mar 2020 16:38:47 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: core: Set port link to RxDetect if port is not
 enabled after resume



> On Mar 6, 2020, at 03:02, Alan Stern <stern@...land.harvard.edu> wrote:
> 
> On Thu, 5 Mar 2020, Kai-Heng Feng wrote:
> 
>> On Dell TB16, Realtek USB ethernet (r8152) connects to an SMSC hub which
>> then connects to ASMedia xHCI's root hub:
>> 
>> /:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M
>>    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/7p, 5000M
>>            |__ Port 2: Dev 3, If 0, Class=Vendor Specific Class, Driver=r8152, 5000M
>> 
>> Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
>> Bus 004 Device 002: ID 0424:5537 Standard Microsystems Corp. USB5537B
>> Bus 004 Device 003: ID 0bda:8153 Realtek Semiconductor Corp. RTL8153 Gigabit Ethernet Adapter
>> 
>> The port is disabled after resume:
>> xhci_hcd 0000:3f:00.0: Get port status 4-1 read: 0x280, return 0x280
>> 
>> According to xHCI 4.19.1.2.1, we should set link to RxDetect to transit
>> it from disabled state to disconnected state, which allows the port to
>> be set to U0 and completes the resume process.
>> 
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>> ---
>> 
>> P.S. This is and differnt (and should be more correct) approach to solve
>> https://lore.kernel.org/lkml/20191129174115.31683-1-kai.heng.feng@canonical.com/
>> 
>> drivers/usb/core/hub.c | 14 +++++++++++++-
>> 1 file changed, 13 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index 54cd8ef795ec..352e33c84d6a 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -3537,12 +3537,24 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg)
>> 
>> 	/* Skip the initial Clear-Suspend step for a remote wakeup */
>> 	status = hub_port_status(hub, port1, &portstatus, &portchange);
>> -	if (status == 0 && !port_is_suspended(hub, portstatus)) {
>> +	if (status == 0 && !port_is_suspended(hub, portstatus)
>> +	    && (portstatus & USB_PORT_STAT_ENABLE)) {
> 
> This doesn't look right.  We want to skip the step the clears the
> port's suspend feature whenever the feature is already clear,
> regardless of whether the port is enabled.
> 
> Besides, isn't this new test racy?  Suppose the port was enabled when
> we called hub_port_status above, but it got disabled in the nanoseconds
> since then?
> 
>> 		if (portchange & USB_PORT_STAT_C_SUSPEND)
>> 			pm_wakeup_event(&udev->dev, 0);
>> 		goto SuspendCleared;
>> 	}
>> 
>> +	/* xHCI 4.19.1.2.1 */
>> +	if (hub_is_superspeed(hub->hdev)) {
>> +		if (!(portstatus & USB_PORT_STAT_ENABLE))
>> +			status = hub_set_port_link_state(hub, port1,
>> +							 USB_SS_PORT_LS_RX_DETECT);
>> +
>> +		if (status)
>> +			dev_dbg(&port_dev->dev,
>> +				"can't set to RxDetect, status %d\n", status);
>> +	}
>> +
> 
> So maybe this part belongs later in the routine.  Or maybe it shouldn't
> be in the hub driver at all -- since it is xHCI-specific, shouldn't it
> go into the xhci-hcd driver?

Ok, I'll put this change into xhci instead. It should also avoid the race
you mentioned above.

Kai-Heng

> 
> Alan Stern
> 
>> 	/* see 7.1.7.7; affects power usage, but not budgeting */
>> 	if (hub_is_superspeed(hub->hdev))
>> 		status = hub_set_port_link_state(hub, port1, USB_SS_PORT_LS_U0);