From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pidgin.makrotopia.org (pidgin.makrotopia.org [185.142.180.65]) (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 E8C286FC7; Fri, 28 Jun 2024 01:11:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.142.180.65 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719537081; cv=none; b=G43UINnsZQOJc4yYF7QfFn3Qow8ECyTLI+5fHBXUXi01C5vc6laGAzU+WHNq94wFnfrjcEMjnC1NEpU4H+7KJETTCjTTdwDli252zrtZyokQVy+exfAm7cdLD+Pr3A8Eiv5t9oc5ymTYJU42qwNYUbyshLLgvXDe/yD7AYzopYs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719537081; c=relaxed/simple; bh=AX6vzRoEhZIXhTB8bmQXDahq6Kmf4gcwbghJqr+xbNo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QokUq3X5ZRfHg7N3FsABrbJXuGk3PSLoNb4TvoxVX+sDfY/fAttKVP3LeEfgua+9CSRwDq/JM4mh17/IQU5CKRZuSKXHf+cpX+NqWlOB8fi2FDT432bsKqayuUBqfhDn4RZV6Tr7a0BetQvMwgiRSbWh3YN1NvNqmXBJr+aBnPg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=makrotopia.org; spf=pass smtp.mailfrom=makrotopia.org; arc=none smtp.client-ip=185.142.180.65 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=makrotopia.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=makrotopia.org Received: from local by pidgin.makrotopia.org with esmtpsa (TLS1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.97.1) (envelope-from ) id 1sN08u-000000000E1-0yNQ; Fri, 28 Jun 2024 01:11:12 +0000 Date: Fri, 28 Jun 2024 02:11:07 +0100 From: Daniel Golle To: Andrew Lunn Cc: Bartosz Golaszewski , Heiner Kallweit , Russell King , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski Subject: Re: [PATCH v2 net-next 3/3] net: phy: aquantia: add support for aqr115c Message-ID: References: <20240627113018.25083-1-brgl@bgdev.pl> <20240627113018.25083-4-brgl@bgdev.pl> 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=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jun 28, 2024 at 02:18:45AM +0200, Andrew Lunn wrote: > On Thu, Jun 27, 2024 at 11:42:45PM +0100, Daniel Golle wrote: > > Hi Bartosz, > > > > On Thu, Jun 27, 2024 at 01:30:17PM +0200, Bartosz Golaszewski wrote: > > > From: Bartosz Golaszewski > > > > > > Add support for a new model to the Aquantia driver. This PHY supports > > > Overlocked SGMII mode with 2.5G speeds. > > > > I don't think that there is such a thing as "Overclocked SGMII mode with > > 2.5G speed". > > Unfortunately, there is. A number of vendors say they do this, without > saying quite what they actually do. As you point out, symbol > replication does not work, and in-band signalling also makes no > sense. So they throw all that away. Leaving just the higher clock > rate, single speed, and no in-band signalling. > > In the end, that looks very similar to 2500BaseX with broken inband > signalling. Let's call it that then: "2500Base-X with broken in-band signalling". MaxLinear describes that quite clearly in their (open!) datasheets[1], and gives some insight into the (mis-)use of the term "SGMII" in the industry as synonymous to just any type of serialized Ethernet MII: " 3.4 SGMII Interface The GPY211 implements a serial data interface, called SGMII or SerDes, to connect to another chip implementing the MAC layer (MAC SoC). " (page 32) Later on they mention that " 3.4.7 Auto-negotiation Modes Supported by SGMII Two modes are supported for the SGMII auto-negotiation protocol: * Cisco* Serial-GMII Specification 1.8 [4] * 1000BX IEEE 802.3 following IEEE Clause 37 [2] " (page 37) Aquantia's datasheets are only available under NDA, so I cannot quote them directly, but I can tell you that their definition of "SGMII" is pretty similar to that of MaxLinear. > > > Hence I assume that what you meant to say here is that the PHY uses > > 2500Base-X as interface mode and performs rate-adaptation for speeds > > less than 2500M (or half-duplex) using pause frames. > > Not all systems assume rate adaptation. Some are known to use SGMII > for 10/100/1G with inband signalling, and then swap to 2500BaseX > without inband-signalling for 2.5G operation! Yes, most 2.5G PHYs out there (MaxLinear, RealTek) actually support both, with interface-mode switching being the better option compared to often rather problematic rate-adaptation... When it comes to Aquantia we are using 2500Base-X with rate adaptation for the older 2.5G PHYs, so I assume the newer ones would not differ in that regard. Or rather: If we were to introduce interface-mode-switching also for the Aquantia 2.5G PHYs then we should try doing it for all of them at least. > > 2.5G is a mess. +1 [1]: https://assets.maxlinear.com/web/documents/617810_gpy211b1vc_gpy211c0vc_ds_rev1.4.pdf