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Message-ID: <e6e063bd-e6da-1b23-b012-e10f7415ab2b@gmail.com> Date: Wed, 11 Dec 2019 22:20:33 +0100 From: Heiner Kallweit <hkallweit1@...il.com> To: Russell King - ARM Linux admin <linux@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com> Cc: netdev@...r.kernel.org Subject: Re: phylib's new dynamic feature detection seems too early On 10.12.2019 18:15, Russell King - ARM Linux admin wrote: > Hi, > > Back in dcdecdcfe1fc ("net: phy: switch drivers to use dynamic feature > detection"), Heiner switched a bunch of PHYs over to using his > wonderful new idea of reading the PHY capabilities from the registers. > However, this is flawed. > > The features are read from the PHY shortly after the PHY driver is > bound to the device, while the PHY is in its default pin-strapped > defined mode. PHYs such as the 88E1111 set their capabilities according > to the pin-strapped host interface mode. > > If the 88E1111 is pin-strapped for a 1000base-X host interface, then it > indicates that it is not capable of 100M or 10M modes - which is > entirely sensible. > > However, the SFP support will switch the PHY into SGMII mode, where the > PHY will support 100M and 10M modes. Indeed, reading the PHY registers > using mii-diag after initialisation reports that the PHY supports these > speeds. > > This switch happens in the Marvell PHY driver when the config_init() > method is called, via phy_init_hw() and phy_attach_direct() - which > is where the MAC driver configures the PHY for its requested interface > mode. > > Therefore, the features dynamically read from the PHY are entirely > meaningless, until the PHY interface mode has been properly set. > > This means that SFP modules, such as Champion One 1000SFPT and a > multitude of others which default to a 1000base-X interface end up > only advertising 1000baseT despite being switched to SGMII mode and > actually supporting 100M and 10M speeds - and that can't be changed > via ethtool as the support mask doesn't allow the other speeds. > > Thoughts how to get around this? > Before reading PHY capabilities from the registers the capabilities were completely static, I don't think this was better. The capabilities read in phy_probe() are correct for the default interface mode. And for all PHY drivers not implementing config_init() we have to read the capabilities in phy_probe(). In case the capabilities can change in config_init() a first thought would be to clear supported/advertised and re-read the capabilities at the end of config_init(). Heiner
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