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 BB6EA2E8B79 for ; Wed, 3 Sep 2025 10:59:58 +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=1756897200; cv=none; b=bOfspR0z/LY/e5ItogPAcgogDQ3y+lXRA+6NUCT0ZAxxs22Lup/N+ZSJYaGHUHncjxWz1GKQbEytlSR4qcTz6QQJwXr8FAtrovaVsU632HoThw22F+SoaKH/DmLCv7tsSCSvRwFl6Ouz0aI1AF3K4HkjNAEx0/ctVACn4mTPtb0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756897200; c=relaxed/simple; bh=pPBDxptN+pKBfE0OGyGISwGzXBA8VZHPd80i8goHzGs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=U9lwseulfQB8rJW/EJ1U+skyjYCuxrZeC/ybuWML700hOnVknb57SekznJ0UE8xnhFw8zdLYmA761zPM1wNQvSo/oWmgIdZl5vDnzrLKRst0QM9oWtWf1s4MJMJxxsVm141HUtikN2BIDM7vch9qUnERtpd61kIVcFStZR1uMQY= 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 1utlDO-0005zA-2Z; Wed, 03 Sep 2025 12:59:46 +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 1utlDK-003Xsx-0i; Wed, 03 Sep 2025 12:59:42 +0200 Received: from ore by pty.whiteo.stw.pengutronix.de with local (Exim 4.96) (envelope-from ) id 1utlDK-00HZBt-0I; Wed, 03 Sep 2025 12:59:42 +0200 Date: Wed, 3 Sep 2025 12:59:42 +0200 From: Oleksij Rempel To: Kory Maincent Cc: Jakub Kicinski , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , Jiri Pirko , Simon Horman , Jonathan Corbet , kernel@pengutronix.de, Dent Project , Thomas Petazzoni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Maxime Chevallier , linux-doc@vger.kernel.org, Kyle Swenson Subject: Re: [PATCH net-next v2 4/4] net: pse-pd: pd692x0: Add devlink interface for configuration save/reset Message-ID: References: <20250829-feature_poe_permanent_conf-v2-0-8bb6f073ec23@bootlin.com> <20250829-feature_poe_permanent_conf-v2-4-8bb6f073ec23@bootlin.com> <20250901133100.3108c817@kernel.org> <20250902164314.12ce43b4@kmaincent-XPS-13-7390> <20250902134212.4ceb5bc3@kernel.org> <20250902134844.7e3593b9@kernel.org> <20250903111025.4642efb7@kmaincent-XPS-13-7390> Precedence: bulk X-Mailing-List: linux-kernel@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: <20250903111025.4642efb7@kmaincent-XPS-13-7390> 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: linux-kernel@vger.kernel.org On Wed, Sep 03, 2025 at 11:10:25AM +0200, Kory Maincent wrote: > On Wed, 3 Sep 2025 09:10:28 +0200 > Oleksij Rempel wrote: > > > On Tue, Sep 02, 2025 at 01:48:44PM -0700, Jakub Kicinski wrote: > > > On Tue, 2 Sep 2025 13:42:12 -0700 Jakub Kicinski wrote: > > > > On Tue, 2 Sep 2025 16:43:14 +0200 Kory Maincent wrote: > > > > > > Sorry for not offering a clear alternative, but I'm not aware of any > > > > > > precedent for treating devlink params as action triggers. devlink > > > > > > params should be values that can be set and read, which is clearly not > > > > > > the case here: > > > > > > > > > > Ok. > > > > > We could save the configuration for every config change and add a > > > > > reset-conf action to devlink reload uAPI? The drawback it that it will > > > > > bring a bit of latency (about 110ms) for every config change. > > > > > > > > > > Or adding a new devlink uAPI like a devlink conf but maybe we don't > > > > > have enough cases to add such generic new uAPI. > > > > > Or get back to the first proposition to use sysfs. > > > > > > > > > > What do you think? > > > > > > > > If you are asking for my real preference, abstracting away whether it's > > > > doable and justifiable amount of effort for you -- I'd explore using > > > > flags in the ethtool header to control whether setting is written to > > > > the flash. > > > > > > PS. failing that the less uAPI the better. Tho, given that the whole > > > point here is giving user the ability to write the flash -- asking for > > > uAPI-light approach feels contradictory. > > > > > > Taking a step back -- the "save to flash" is something that OEM FW > > > often supports. But for Linux-based control the "save to flash" should > > > really be equivalent to updating some user space config. When user > > > configures interfaces in OpenWRT we're not flashing them into the > > > device tree... Could you perhaps explain what makes updating the > > > in-flash config a high-priority requirement for PoE? > > > > > > > I think the main use case question is: what happens if the application > > CPU reboots? > > Do we go back to “safe defaults”? But what are safe defaults - that can > > vary a lot between systems. > > In case of CPU reboot, the port matrix will be flashed, which means the > controller is restarted and the ports get disconnected. > Therefore indeed we will go back to default settings. > > > In many setups, if the CPU reboots it also means the bridge is down, so > > there is no packet forwarding. In that case, does it even make sense to > > keep providing PoE power if the networking part is non-functional? > > It depends, we might not want to reboot the Powered Devices if the switch > reboot. I don't currently have specific case in mind which could need this > behavior. > Mainly, the Dent Project final aim was to support mainline all the features > supported in their poed tool. > https://github.com/dentproject/poed/blob/main/dentos-poe-agent/opt/poeagent/docs/Userguide > > > Another angle: does it make sense to overwrite the hardware power-on > > defaults each time the system starts? Or should we rather be able to > > read back the stored defaults from the hardware into the driver and work > > with them? > > Yes that is one of the design proposition, but we will still need a way to > reset the conf as said before. > > > Does anyone here have field experience with similar devices? How are > > these topics usually handled outside of my bubble? > > Kyle any field experience on this? I can confirm a field case from industrial/medical gear. Closed system, several modules on SPE, PoDL for power. Requirement: power the PDs as early as possible, even before Linux. The box boots faster if power-up and Linux init run in parallel. In this setup the power-on state is pre-designed by the product team and should not be changed by Linux at runtime. So the question is how to communicate and control this: Option A - Vendor tool writes a fixed config to NVM (EEPROM) Pro: matches "pre-designed, don't touch" model; PDs come up early without Linux. Con: needs extra vendor tooling; hard to keep in sync with what userspace shows; Linux may not know what is in NVM unless we read/reflect it. Option B - Do all changes in RAM, then one explicit "commit to NVM" Pro: one write; predictable latency hit only on commit; maps to a "transaction/commit" model. Con: what if the controller discarded some changes during the session? We would need a clear commit status and a way to report which settings actually stuck. Option C - Write-through: every change also goes to NVM Pro: if the system resets, config is always up to date. Con: adds about 50-110 ms per change on this hardware; may be too slow for interactive tools or batch reconfig. >From API side, if write-through is possible on this hardware, we can likely make this per-port and per-setting: ethtool per-port setters can take a "persist=1" flag. Driver applies the change and also writes it to NVM for that port. If a particular setting (bit/field) cannot be persisted by the controller/NVM, the driver returns an error for the whole request. Userspace then knows persistence is not supported for that item. Factory reset: If hardware supports per-port defaults in NVM, provide a per-port factory_reset op. Do PD692x0 supports per-port save/restore functionality? 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 |