Re: [PATCH v5 3/6] net: phy: at803x: add QCA8084 ethernet phy support

[Jie Luo]

On 11/23/2023 8:01 PM, Russell King (Oracle) wrote:
> On Thu, Nov 23, 2023 at 06:57:59PM +0800, Jie Luo wrote:
> > On 11/21/2023 7:52 PM, Russell King (Oracle) wrote:
> > > Ultimately, you will need a way to use inband signalling with Cisco
> > > SGMII for 10M/100M/1G speeds, and then switch to 2500base-X when
> > > operating at 2.5G speeds, and that is done via the PHY driver
> > > updating phydev->interface.
> > >
> > > What we do need is some way for the PHY to also tell the PCS/MAC
> > > whether inband should be used. This is something I keep bringing up
> > > and now that we have PCS drivers revised to use the value from
> > > phylink_pcs_neg_mode() _and_ a consistent implementation amongst them
> > > we can now think about signalling to PCS drivers whether inband mode
> > > needs to be turned off when switching between modes.
> >
> > Yes, we can switch the interface mode according to the current link
> > speed in the pcs driver.
> > but the issue is that the phy-mode i specified for the PHYLINK,
> > if phy-mode is sgmii, the support capability is limited to maximum
> > capability 1G during the PHYLINK setup and i can't configure it to 2.5G
> > dynamically, if the phy-mode is 2500base-x, then PHY capability will
> > be modified to only support 2.5G, other speeds can't be linked up.
>
> So you need my patches that add "possible_interfaces" to phylib so you
> can tell phylink that you will be switching between SGMII and
> 2500base-X. Please see the RFC posting of those patches I sent
> yesterday and try them out - you will need to modify your phylib
> driver to fill in phydev->possible_interfaces.

Your patches work on my board, thanks Russell.

> > > There have been patches in the past that allow inband mode to be
> > > queried from phylib, and this is another important component in
> > > properly dealing with PHYs that need to use inband signalling with
> > > Cisco SGMII, but do not support inband signalling when operating at
> > > 2.5G speeds. The problem when operating at 2.5G speed is that the
> > > base-X protocols are normally for use over fibre, which is the media,
> > > and therefore the ethtool Autoneg bit should define whether inband
> > > gets used or not. However, in the case of a PHY using 2500base-X,
> > > the Autoneg bit continues to define whether autonegotiation should
> > > be used on the media, and in this case it's the media side of the
> > > PHY rather than the 2500base-X link.
> > >
> > > So, when using a 2500base-X link to a PHY, we need to disregard the
> > > Autoneg bit, but that then raises the question about how we should
> > > configure it - and one solution to that would be to entire of phylib
> > > what the PHY wants to do. Another is to somehow ask the PCS driver
> > > whether it supports inband signalling at 2500base-X, and resolve
> > > those capabilities.
> >
> > For the qca808x PHY, when it is linked in 2.5G, the autoneg is also
> > disabled in PCS hardware, so the sgmii+ of qca808x PHY is almost
> > same as 2500base-X.
>
> Not "almost". It _is_ the same. This is the point I've been trying
> to get across to you. Without inband signalling, 1000base-X and SGMII
> (when operating at 1G) are _identical_ and entirely compatible.
>
> You've said that your 2.5G "SGMII" mode has inband signalling disabled,
> and thus it without inband signalling, 2500base-X and this 2.5G mode
> are again identical and entirely compatible. There's no "almost" about
> it.
Yes, confirmed with HW guy, they work on the same way.