From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: Mathias Nyman <mathias.nyman@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Stern <stern@rowland.harvard.edu>,
AceLan Kao <acelan.kao@canonical.com>,
USB list <linux-usb@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] xhci: Wait until link state trainsits to U0 after setting USB_SS_PORT_LS_U0
Date: Tue, 14 Jan 2020 16:48:40 +0200 [thread overview]
Message-ID: <7f6d4742-6e68-ea1d-4266-c69c27a19df6@linux.intel.com> (raw)
In-Reply-To: <CAAd53p56oXDsPBKqZA_HJbtajWNBQz_LfK-fpOiuxoTrn3WU5w@mail.gmail.com>
On 13.1.2020 11.18, Kai-Heng Feng wrote:
> On Fri, Jan 10, 2020 at 11:27 PM Mathias Nyman
> <mathias.nyman@linux.intel.com> wrote:
>>
>> On 3.1.2020 10.40, Kai-Heng Feng wrote:
>>> Like U3 case, xHCI spec doesn't specify the upper bound of U0 transition
>>> time. The 20ms is not enough for some devices.
>>>
>>> Intead of polling PLS or PLC, we can facilitate the port change event to
>>> know that the link transits to U0 is completed.
>>>
>>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
>>> ---
>>> drivers/usb/host/xhci-hub.c | 8 +++++++-
>>> drivers/usb/host/xhci-mem.c | 1 +
>>> drivers/usb/host/xhci-ring.c | 1 +
>>> drivers/usb/host/xhci.h | 1 +
>>> 4 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
>>> index 2b2e9d004dbf..07886a1bce62 100644
>>> --- a/drivers/usb/host/xhci-hub.c
>>> +++ b/drivers/usb/host/xhci-hub.c
>>> @@ -1310,11 +1310,17 @@ int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
>>> spin_lock_irqsave(&xhci->lock, flags);
>>> }
>>> }
>>> + if (link_state == USB_SS_PORT_LS_U0)
>>> + reinit_completion(&ports[wIndex]->link_state_changed);
>>
>> All the other suspend and resume related port flags/completions are
>> in struct xhci_bus_state. See for example rexit_done[].
>> Not sure that is a better place but at least it would be consistent.
>>
>> Could actually make sense to move more of them to the xhci_port structure,
>> but perhaps in some later suspend/resume rework patch.
>
> Ok. Should I keep this part of the patch as is? Or move it to
> xhci_bus_state and probably move it back to xhci_port in later rework
> patch?
Maybe move it to xhci_bus_state for now.
>
>>>
>>> xhci_set_link_state(xhci, ports[wIndex], link_state);
>>>
>>> spin_unlock_irqrestore(&xhci->lock, flags);
>>> - msleep(20); /* wait device to enter */
>>> + if (link_state == USB_SS_PORT_LS_U0) {
>>> + if (!wait_for_completion_timeout(&ports[wIndex]->link_state_changed, msecs_to_jiffies(100)))
>>> + xhci_dbg(xhci, "missing U0 port change event for port %d-%d\n", hcd->self.busnum, wIndex + 1);
>>
>> We might be waiting for completion here in unnecessary.
>> No completion is called if port is already in U0, either set by
>> xhci_bus_resume(), or we race with a device initiated resume.
>
> Is there a way to know if device initiated resume is inplace?
Yes, before xhci interrupt handler handles the device initiated resume PLS
is XDEV_RESUME and PLC is set.
After the interrupt handler PLS goes from XDEV_RESUME to XDEV_RECOVERY to XDEV_U0.
A bit is set for bus_state->port_remote_wakeup, and on usb core side
also bus->resuming_ports |= bit is set, (having both may be a bit redundant, we might
be able to get rid of bus_state->port_remote_wakeup, but not right now)
>
>>
>> Maybe read the current port link state first, and don't do anything if it's
>> already in U0, or fail if it's in a state where we can't resume to U0.
>
> What happens if device initiated resume happens right after we query the PLS?
Not sure, fortunately the drivers task is to write XDEV_U0 to PLS both when
we want a host initiated resume, or when we want to react on a device initiated
resume. So hopefully that's ok, but this race exists.
Better keep calling completion for both host and device initiated resume cases
when port reaches U0/U1/U2 to avoid waiting for the completion unnecessary,
like you current patch does.
-Mathias
next prev parent reply other threads:[~2020-01-14 14:46 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-03 8:40 [PATCH 1/3] xhci: Ensure link state is U3 after setting USB_SS_PORT_LS_U3 Kai-Heng Feng
2020-01-03 8:40 ` [PATCH 2/3] xhci: Wait until link state trainsits to U0 after setting USB_SS_PORT_LS_U0 Kai-Heng Feng
2020-01-10 15:29 ` Mathias Nyman
2020-01-13 9:18 ` Kai-Heng Feng
2020-01-14 14:48 ` Mathias Nyman [this message]
2020-01-03 8:40 ` [PATCH 3/3] USB: Disable LPM on WD19's Realtek Hub during setting its ports to U0 Kai-Heng Feng
2020-01-03 15:21 ` Alan Stern
2020-01-03 16:25 ` Kai-Heng Feng
2020-01-03 16:54 ` Alan Stern
2020-01-04 6:41 ` Kai-Heng Feng
2020-01-04 16:20 ` Alan Stern
2020-01-06 6:19 ` Kai-Heng Feng
2020-01-06 15:08 ` Alan Stern
2020-01-10 7:35 ` Kai-Heng Feng
2020-01-10 8:02 ` [PATCH v2 3/3] USB: Disable LPM on WD19's Realtek Hub Kai-Heng Feng
2020-01-10 15:40 ` Alan Stern
2020-01-10 15:51 ` Kai-Heng Feng
2020-01-10 16:36 ` Alan Stern
2020-01-10 16:46 ` Kai-Heng Feng
2020-01-11 19:23 ` Greg KH
2020-01-13 9:06 ` Kai-Heng Feng
2020-01-10 9:34 ` [PATCH 1/3] xhci: Ensure link state is U3 after setting USB_SS_PORT_LS_U3 Mathias Nyman
2020-01-13 9:10 ` Kai-Heng Feng
2020-01-14 15:07 ` Mathias Nyman
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