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SubjectRe: [PATCH 3/3] USB: Disable LPM on WD19's Realtek Hub during setting its ports to U0
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Hi Alan,

> On Jan 3, 2020, at 23:21, Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Fri, 3 Jan 2020, Kai-Heng Feng wrote:
>
>> Realtek Hub (0bda:0x0487) used in Dell Dock WD19 sometimes drops off the
>> bus when bringing underlying ports from U3 to U0.
>>
>> After some expirements and guessworks, the hub itself needs to be U0
>> during setting its port's link state back to U0.
>>
>> So add a new quirk to let the hub disables LPM on setting U0 for its
>> downstream facing ports.
>>
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
>> ---
>> drivers/usb/core/hub.c | 12 ++++++++++--
>> drivers/usb/core/quirks.c | 7 +++++++
>> include/linux/usb/quirks.h | 3 +++
>> 3 files changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index f229ad6952c0..35a035781c5a 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -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)?

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.

>
>> + }
>> + } else
>> status = usb_clear_port_feature(hub->hdev,
>> port1, USB_PORT_FEAT_SUSPEND);
>> if (status) {
>> diff --git a/drivers/usb/core/quirks.c b/drivers/usb/core/quirks.c
>> index 6b6413073584..69474d0d2b38 100644
>> --- a/drivers/usb/core/quirks.c
>> +++ b/drivers/usb/core/quirks.c
>> @@ -131,6 +131,9 @@ static int quirks_param_set(const char *val, const struct kernel_param *kp)
>> case 'o':
>> flags |= USB_QUIRK_HUB_SLOW_RESET;
>> break;
>> + case 'p':
>> + flags |= USB_QUIRK_DISABLE_LPM_ON_U0;
>> + break;
>
> The new 'p' flag needs to be documented.

Yes I missed that, will add in v2.

Kai-Heng

>
> Alan Stern

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