On Thu, Mar 25, 2021 at 12:45:25AM +0100, Marek Behún wrote: > On Wed, 24 Mar 2021 16:16:41 -0700 > Florian Fainelli <f.fainelli@xxxxxxxxx> wrote: > > > On 3/24/2021 4:00 PM, Marek Behún wrote: > > > On Wed, 24 Mar 2021 14:19:28 -0700 > > > Florian Fainelli <f.fainelli@xxxxxxxxx> wrote: > > > > > >>> Another problem is that if lower modes are supported, we should > > >>> maybe use them in order to save power. > > >> > > >> That is an interesting proposal but if you want it to be truly valuable, > > >> does not that mean that an user ought to be able to switch between any > > >> of the supported PHY <=> MAC interfaces at runtime, and then within > > >> those interfaces to the speeds that yield the best power savings? > > > > > > If the code determines that there are multiple working configurations, > > > it theoretically could allow the user to switch between them. > > > > > > My idea was that this should be done by kernel, though. > > > > > > But power saving is not the main problem I am trying to solve. > > > What I am trying to solve is that if a board does not support all modes > > > supported by the MAC and PHY, because they are not wired or something, > > > we need to know about that so that we can select the correct mode for > > > PHYs that change this mode at runtime. > > > > OK so the runtime part comes from plugging in various SFP modules into a > > cage but other than that, for a "fixed" link such as a SFF or a soldered > > down PHY, do we agree that there would be no runtime changing of the > > 'phy-mode'? > > No, we do not. The PHY can be configured (by strapping pins or by > sw) to change phy-mode depending on the autonegotiated copper speed. > > So if you plug in an ethernet cable where on the otherside is only 1g > capable device, the PHY will change mode to sgmii. But if you then plug > a 5g capable device, the PHY will change mode to 5gbase-r. > > This happens if the PHY is configured into one of these changing > configurations. It can also be configured to USXGMII, or 10GBASER with > rate matching. > > Not many MACs in kernel support USXGMII currently. > > And if you use rate matching mode, and the copper side is > linked in lower speed (2.5g for example), and the MAC will start > sending too many packets, the internal buffer in the PHY is only 16 KB, > so it will fill up quickly. So you need pause frames support. But this > is broken for speeds <= 1g, according to erratum. Also, the sending of pause frames is only supported for 88x3310P devices, not the 88x3310. The plain 88x3310 requires the MAC to rate-limit in this mode. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
