From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9AC69C2D0C2 for ; Fri, 3 Jan 2020 16:54:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C5A021734 for ; Fri, 3 Jan 2020 16:54:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728061AbgACQyG (ORCPT ); Fri, 3 Jan 2020 11:54:06 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:34940 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1727952AbgACQyG (ORCPT ); Fri, 3 Jan 2020 11:54:06 -0500 Received: (qmail 5175 invoked by uid 2102); 3 Jan 2020 11:54:05 -0500 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 3 Jan 2020 11:54:05 -0500 Date: Fri, 3 Jan 2020 11:54:05 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Kai-Heng Feng cc: Mathias Nyman , , , , Subject: Re: [PATCH 3/3] USB: Disable LPM on WD19's Realtek Hub during setting its ports to U0 In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Sat, 4 Jan 2020, Kai-Heng Feng wrote: > Hi Alan, > > > On Jan 3, 2020, at 23:21, Alan Stern 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 > >> --- > >> 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)? 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? Alan Stern