From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 712A5248F60; Tue, 15 Jul 2025 17:48:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752601733; cv=none; b=ei/gK1y/lcUtuhCPMFpAkdppAREWSir6+mRtnCkIM8R9rJVY/aqNG64n/uFsFyAmHI3aFRMiXZYYjyKxQ4qpW38em/G8pkBaYiUIEeQ4Ow3pbHB483SXi1TwT0omnSqtz5C44OV84UN2oYMZ3zqualwd019xEfBM0Avg3V6HQUw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752601733; c=relaxed/simple; bh=wdfyaBEFuI+Se186ARLt/uqIgP2VA5aMHlBe67qs7ZA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ktrvrwaHPAaa/LoSYJMrVJiHq7Wp/QX729YRAYpqEpKZZtqhuzmnXyS8jedJPP5j5wvOlKRNMUEI6V8azbTHC8oBMo/03tYjQfyVR8ZYftf1YLjm5RGSPudgi4S8q+vff1k+wkRLGTD80OGRbuSezbHm/5S3nh0+q6psFApeZsU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=BlGOyJry; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="BlGOyJry" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B2196C4CEE3; Tue, 15 Jul 2025 17:48:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1752601733; bh=wdfyaBEFuI+Se186ARLt/uqIgP2VA5aMHlBe67qs7ZA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BlGOyJryrZDa4TqzMz/pCGDPzzGbQGVtHd5Ui64X4fTk49zFcMrgdclLLP7S5OqYj 86SH3pyTEK4PCvTpc4YSBAKOnEk5SDKcPr0s9gWHfcz/tQfzvLHSq4G8TzAV3Z3ScB 1aDAo8YJxjdhAfqEArm6QBPcaTmmUZXqpDaL+KCk= Date: Tue, 15 Jul 2025 19:48:50 +0200 From: Greg KH To: Mathias Nyman , stern@rowland.harvard.edu Cc: linux-usb@vger.kernel.org, stable@vger.kernel.org, =?utf-8?Q?=C5=81ukasz?= Bartosik Subject: Re: [PATCH] usb: hub: Don't try to recover devices lost during warm reset. Message-ID: <2025071527-vendor-rockfish-ef19@gregkh> References: <20250623133947.3144608-1-mathias.nyman@linux.intel.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250623133947.3144608-1-mathias.nyman@linux.intel.com> On Mon, Jun 23, 2025 at 04:39:47PM +0300, Mathias Nyman wrote: > Hub driver warm-resets ports in SS.Inactive or Compliance mode to > recover a possible connected device. The port reset code correctly > detects if a connection is lost during reset, but hub driver > port_event() fails to take this into account in some cases. > port_event() ends up using stale values and assumes there is a > connected device, and will try all means to recover it, including > power-cycling the port. > > Details: > This case was triggered when xHC host was suspended with DbC (Debug > Capability) enabled and connected. DbC turns one xHC port into a simple > usb debug device, allowing debugging a system with an A-to-A USB debug > cable. > > xhci DbC code disables DbC when xHC is system suspended to D3, and > enables it back during resume. > We essentially end up with two hosts connected to each other during > suspend, and, for a short while during resume, until DbC is enabled back. > The suspended xHC host notices some activity on the roothub port, but > can't train the link due to being suspended, so xHC hardware sets a CAS > (Cold Attach Status) flag for this port to inform xhci host driver that > the port needs to be warm reset once xHC resumes. > > CAS is xHCI specific, and not part of USB specification, so xhci driver > tells usb core that the port has a connection and link is in compliance > mode. Recovery from complinace mode is similar to CAS recovery. > > xhci CAS driver support that fakes a compliance mode connection was added > in commit 8bea2bd37df0 ("usb: Add support for root hub port status CAS") > > Once xHCI resumes and DbC is enabled back, all activity on the xHC > roothub host side port disappears. The hub driver will anyway think > port has a connection and link is in compliance mode, and hub driver > will try to recover it. > > The port power-cycle during recovery seems to cause issues to the active > DbC connection. > > Fix this by clearing connect_change flag if hub_port_reset() returns > -ENOTCONN, thus avoiding the whole unnecessary port recovery and > initialization attempt. > > Cc: stable@vger.kernel.org > Fixes: 8bea2bd37df0 ("usb: Add support for root hub port status CAS") > Tested-by: Łukasz Bartosik > Signed-off-by: Mathias Nyman > --- > drivers/usb/core/hub.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) Alan, any objection to this? thanks, greg k-h