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 7DC7222A4F6 for ; Fri, 18 Jul 2025 07:39:01 +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=1752824343; cv=none; b=t6NP4eHTNUf1Nz5QdPQsZcUzsW5jciMUG4f6AtizfITkYjl4Skitmwo6TMRs3DC2rOG0TtFKrQ5VnyLSthQ3dgP569WJElJvhaWoyrLCDFhMvsEXmAtXgwZCQrGwEIHs5+vCibh+ns6oLqsFxnteDZOGngR55lWZXwkz23V0kjo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752824343; c=relaxed/simple; bh=kZ0savlK8hmTukJ61RLvHvHkzYy+aZT8mFDG44NLLIs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JzJuzf5I4TZRWYIHPnXlYtp9nrpwpX5uBSKPgMHwA1jk0Sizg+p1VQ+kt2tBlsRL31PAIRZKZwi0AdKYABY2zWP2TPCENrJzgUhNfJ343yfiRvTrhXPnUp/5PqhJ7O78EdKgl36nig+PbzXFnaiMKk32S/VmFC/T0non11q94c4= 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 1ucffU-0005ix-MH; Fri, 18 Jul 2025 09:38:08 +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 1ucffP-0092TR-0n; Fri, 18 Jul 2025 09:38:03 +0200 Received: from ore by pty.whiteo.stw.pengutronix.de with local (Exim 4.96) (envelope-from ) id 1ucffP-008KaQ-0N; Fri, 18 Jul 2025 09:38:03 +0200 Date: Fri, 18 Jul 2025 09:38:03 +0200 From: Oleksij Rempel To: "Russell King (Oracle)" Cc: Andrew Lunn , Heiner Kallweit , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Rob Herring , Krzysztof Kozlowski , Florian Fainelli , Maxime Chevallier , Kory Maincent , Lukasz Majewski , Jonathan Corbet , kernel@pengutronix.de, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Divya.Koppera@microchip.com Subject: Re: [PATCH net-next v1 1/1] Documentation: networking: add detailed guide on Ethernet flow control configuration Message-ID: References: <20250717103702.2112988-1-o.rempel@pengutronix.de> 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 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 Thu, Jul 17, 2025 at 06:29:53PM +0100, Russell King (Oracle) wrote: > On Thu, Jul 17, 2025 at 12:37:02PM +0200, Oleksij Rempel wrote: > > +Changing the Settings > > +--------------------- > > +Use `ethtool -A ` to change the settings. > > + > > +.. code-block:: bash > > + > > + # Enable RX and TX pause, with autonegotiation > > + ethtool -A eth0 autoneg on rx on tx on > > + > > + # Force RX pause on, TX pause off, without autonegotiation > > + ethtool -A eth0 autoneg off rx on tx off > > + > > +**Key Configuration Concepts**: > > + > > +* **Autonegotiation Mode**: The recommended mode. The driver programs the PHY > > + to *advertise* the `rx` and `tx` capabilities. The final active state is > > + determined by what both sides of the link agree on. > > I'm not sure one cal call this "recommended mode", because it doesn't. > If one specifies tx=0 rx=1, one would expect that the "recommend mode" > would be tx=0 and rx=1, but if the link partner supports symmetric > pause, you actually end up with tx=1 and rx=1. If the link partner > supports only asymmetric, then you end up with tx=0 rx=1 as requested. > > Perversely, if you specify tx=1 rx=1, then if the remote supports only > asymmetric, you end up with everything disabled. Only tx=1 rx=1 is > supported in this configuration, you can't end up with anything else. > > Basically, I don't think calling it "recommended" works. Ack, I'll drop "recommended". Would it make sense to also add a short note about the limitations of link-level flow control? For example, how pause frames can interfere with traffic prioritization and QoS mechanisms. -- 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 |