From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from metis.whiteo.stw.pengutronix.de (metis.whiteo.stw.pengutronix.de [185.203.201.7]) (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 8A61128134C for ; Tue, 16 Sep 2025 07:18:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.203.201.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758007116; cv=none; b=JCUqrvM2ZaQxgIq5uYDsG4p9oSQSiLw4f2T9XcpM+NwBlwLrGgLITD0xKKhio4b1iaD1LQQ0iwgBSjWKINUjIcf7BVf65/BT3TjgjJtha4swo5xWmcPQmr8yBN9LJ+h0JP0xv4JrYbu0F3mcnI7LPfIsowzFyOmAayOAOZsDf8c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758007116; c=relaxed/simple; bh=/n5L0zuim9T9324maodQZtpPeiOd0fceXfQP+n+Thx0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Poe/qae0mSz6jGO7jBek+Nku9Dy7T1vPxUJzSSJrq0iZ5eLx0oGxo3o9D3kOoVhd6/EjT0w6Nat1qXPusfKR0eIUlLbGMw4tdodM4/geQFJOAVzCdYEoAHaV8LbMsu5nVs7wJkEUwtStrNf1pwc4ko78GDwc8IFzanw5Uasu9Jc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de; spf=pass smtp.mailfrom=pengutronix.de; arc=none smtp.client-ip=185.203.201.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pengutronix.de Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1uyPx6-0007Fb-L3; Tue, 16 Sep 2025 09:18:12 +0200 Received: from pty.whiteo.stw.pengutronix.de ([2a0a:edc0:2:b01:1d::c5]) by drehscheibe.grey.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1uyPx4-001Y7t-0T; Tue, 16 Sep 2025 09:18:10 +0200 Received: from ore by pty.whiteo.stw.pengutronix.de with local (Exim 4.96) (envelope-from ) id 1uyPx3-00BTqe-3A; Tue, 16 Sep 2025 09:18:10 +0200 Date: Tue, 16 Sep 2025 09:18:09 +0200 From: Oleksij Rempel To: Alan Stern Cc: "Russell King (Oracle)" , Jakub Kicinski , Marek Szyprowski , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , Hubert =?utf-8?Q?Wi=C5=9Bniewski?= , stable@vger.kernel.org, kernel@pengutronix.de, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Lukas Wunner , Xu Yang , linux-usb@vger.kernel.org Subject: Re: [PATCH net v1 1/1] net: usb: asix: ax88772: drop phylink use in PM to avoid MDIO runtime PM wakeups Message-ID: References: <20250911075513.1d90f8b0@kernel.org> <22773d93-cbad-41c5-9e79-4d7f6b9e5ec0@rowland.harvard.edu> Precedence: bulk X-Mailing-List: netdev@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: X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: ore@pengutronix.de X-SA-Exim-Scanned: No (on metis.whiteo.stw.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: netdev@vger.kernel.org On Sat, Sep 13, 2025 at 08:45:05AM +0200, Oleksij Rempel wrote: > On Fri, Sep 12, 2025 at 03:37:52PM +0100, Russell King (Oracle) wrote: > > On Fri, Sep 12, 2025 at 10:29:47AM -0400, Alan Stern wrote: > > > On Fri, Sep 12, 2025 at 09:33:05AM +0100, Russell King (Oracle) wrote: > > > > On Thu, Sep 11, 2025 at 10:30:09PM -0400, Alan Stern wrote: > > > > > The USB subsystem uses only one pair of callbacks for suspend and resume > > > > > because USB hardware has only one suspend state. However, the callbacks > > > > > do get an extra pm_message_t parameter which they can use to distinguish > > > > > between system sleep transitions and runtime PM transitions. > > > > > > > > Unfortunately, this isn't the case. While a struct usb_device_driver's > > > > suspend()/resume() methods get the pm_message_t, a struct usb_driver's > > > > suspend()/resume() methods do not: > > > > > > > > static int usb_resume_interface(struct usb_device *udev, > > > > struct usb_interface *intf, pm_message_t msg, int reset_resume) > > > > { > > > > struct usb_driver *driver; > > > > ... > > > > if (reset_resume) { > > > > if (driver->reset_resume) { > > > > status = driver->reset_resume(intf); > > > > ... > > > > } else { > > > > status = driver->resume(intf); > > > > > > > > vs > > > > > > > > static int usb_resume_device(struct usb_device *udev, pm_message_t msg) > > > > { > > > > struct usb_device_driver *udriver; > > > > ... > > > > if (status == 0 && udriver->resume) > > > > status = udriver->resume(udev, msg); > > > > > > > > and in drivers/net/usb/asix_devices.c: > > > > > > > > static struct usb_driver asix_driver = { > > > > ... > > > > .suspend = asix_suspend, > > > > .resume = asix_resume, > > > > .reset_resume = asix_resume, > > > > > > > > where asix_resume() only takes one argument: > > > > > > > > static int asix_resume(struct usb_interface *intf) > > > > { > > > > > > Your email made me go back and check the code more carefully, and it > > > turns out that we were both half-right. :-) > > > > > > The pm_message_t argument is passed to the usb_driver's ->suspend > > > callback in usb_suspend_interface(), but not to the ->resume callback in > > > usb_resume_interface(). Yes, it's inconsistent. > > > > > > I suppose the API could be changed, at the cost of updating a lot of > > > drivers. But it would be easier if this wasn't necessary, if there was > > > some way to work around the problem. Unfortunately, I don't know > > > anything about how the network stack handles suspend and resume, or > > > what sort of locking it requires, so I can't offer any suggestions. > > > > I, too, am unable to help further as I have no bandwidth available > > to deal with this. Sorry. > > Thanks for all the valuable input. > > I’ll process the feedback and investigate possible ways to proceed. As a > first step I’ll measure the actual power savings from USB auto-suspend > on AX88772 to see if runtime PM is worth the added complexity. I ran quick power measurements to check whether USB autosuspend is worth the added complexity. Meaning: - "admin up/down" = ip link set dev up/down. - No link partner was attached, so the physical link was down in all tests. Setups: - Debian 5.10 (USB autosuspend present, no phylib). - Debian 6.1 (phylib present, no regression). - Power meter: Fnirsi FNB58. - Env: QEMU 9.2.1 (USB passthrough) xHCI host Intel 100/C230 device ASIX AX88772B (0b95:772b) Legend: - "RT: active" = runtime PM on; - "RT: suspended" = runtime PM auto (device suspended). Results: - Kernel 5.10.237-1 admin up (link down): 0.453 W (RT: active) admin down: 0.453 W (RT: active) admin down: 0.453 W (RT: suspended) - Kernel 6.1.148-1 admin up (link down): 0.453 W (RT: active) admin down: 0.248 W (RT: active) admin down: 0.248 W (RT: suspended) Observations: In this setup, USB autosuspend did not reduce power further (admin-down power is identical with/without autosuspend). The drop from ~0.453 W -> ~0.248 W on 6.1 appears to come from the phylib migration (PHY powered down on admin-down), not from autosuspend. Proposal: Given autosuspend brings no measurable benefit here, and it hasn’t been effectively functional for this device in earlier kernels, I suggest a minimal -stable patch that disables USB autosuspend for ASIX driver to avoid the PM/RTNL/MDIO issues. If someone needs autosuspend-based low-power later, they can implement a proper device low-power sequence and re-enable it. Would this minimal -stable patch be acceptable? Best Regards, Oleksij -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |