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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 7BEB6C2D0C2 for ; Sat, 4 Jan 2020 16:21:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5614C22B48 for ; Sat, 4 Jan 2020 16:21:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726263AbgADQU7 (ORCPT ); Sat, 4 Jan 2020 11:20:59 -0500 Received: from netrider.rowland.org ([192.131.102.5]:39433 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726005AbgADQU7 (ORCPT ); Sat, 4 Jan 2020 11:20:59 -0500 Received: (qmail 7682 invoked by uid 500); 4 Jan 2020 11:20:57 -0500 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 4 Jan 2020 11:20:57 -0500 Date: Sat, 4 Jan 2020 11:20:57 -0500 (EST) From: Alan Stern X-X-Sender: stern@netrider.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: <97F72C66-8D9B-4316-B096-1993FD18CF56@canonical.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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