From: Alan Stern <stern@rowland.harvard.edu>
To: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: Mathias Nyman <mathias.nyman@intel.com>,
<gregkh@linuxfoundation.org>, <acelan.kao@canonical.com>,
<linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] USB: Disable LPM on WD19's Realtek Hub during setting its ports to U0
Date: Sat, 4 Jan 2020 11:20:57 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.2001041117130.7125-100000@netrider.rowland.org> (raw)
In-Reply-To: <97F72C66-8D9B-4316-B096-1993FD18CF56@canonical.com>
On Sat, 4 Jan 2020, Kai-Heng Feng wrote:
> >>>> @@ -3533,9 +3533,17 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg)
> >>>> }
> >>>>
> >>>> /* see 7.1.7.7; affects power usage, but not budgeting */
> >>>> - if (hub_is_superspeed(hub->hdev))
> >>>> + if (hub_is_superspeed(hub->hdev)) {
> >>>> + if (hub->hdev->quirks & USB_QUIRK_DISABLE_LPM_ON_U0) {
> >>>> + usb_lock_device(hub->hdev);
> >>>> + usb_unlocked_disable_lpm(hub->hdev);
> >>>> + }
> >>>> status = hub_set_port_link_state(hub, port1, USB_SS_PORT_LS_U0);
> >>>> - else
> >>>> + if (hub->hdev->quirks & USB_QUIRK_DISABLE_LPM_ON_U0) {
> >>>> + usb_unlocked_enable_lpm(hub->hdev);
> >>>> + usb_unlock_device(hub->hdev);
> >>>
> >>> The locking here seems questionable. Doesn't this code sometimes get
> >>> called with the hub already locked? Or with the child device locked
> >>> (in which case locking the hub would violate the normal locking order:
> >>> parent first, child second)?
> >
> > I did a little checking. In many cases the child device _will_ be
> > locked at this point.
> >
> >> Maybe introduce a new lock? The lock however will only be used by this specific hub.
> >> But I still want the LPM can be enabled for this hub.
> >
> > Do you really need to lock the hub at all? What would the lock protect
> > against?
>
> There can be multiple usb_port_resume() run at the same time for different ports, so this is to prevent LPM enable/disable race.
But there can't really be an LPM enable/disable race, can there? The
individual function calls are protected by the bandwidth mutex taken by
the usb_unlocked_{en|dis}able_lpm routines, and the overall LPM setting
is controlled by the hub device's lpm_disable_counter.
So I think you don't need to lock the hub here.
Alan Stern
next prev parent reply other threads:[~2020-01-04 16:21 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
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 [this message]
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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