On Wed, 24 Mar 2021 17:11:25 -0700 Florian Fainelli <f.fainelli@xxxxxxxxx> wrote: > On 3/24/2021 4:45 PM, 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. > > > > So you really want to change modes. The rate matching mode is > > basically useless. > > OK, so whenever there is a link change you are presumably reading the > mode in which the PHY has been reconfigured to, asking the MAC to > configured itself appropriately based on that, and if there is no > intersection, error out? No. At initialization I tell the PHY to change between 10gbase-r / 5gbase-r / 2500base-x / sgmii according to the copper side. The PHY will do this alone on change on copper side. I don't need to do this. (This already works with current version of marvell10g driver - but kernel is not configuring this, it has to be configure via strapping pins.) But I can tell the PHY at initialization to change instead between xaui / 5gbase-r / 2500base-x / sgmii Again the PHY will do this on its own whenever speed on the copper side changes. But I need to know which of this settings I should use. Marek
