On Fri, Jun 23, 2023 at 03:29:13PM +0200, Andrew Lunn wrote: > On Fri, Jun 23, 2023 at 12:28:49PM +0000, Revanth Kumar Uppala wrote: > > > > > > > -----Original Message----- > > > From: Andrew Lunn <andrew@xxxxxxx> > > > Sent: Wednesday, June 21, 2023 11:00 PM > > > To: Revanth Kumar Uppala <ruppala@xxxxxxxxxx> > > > Cc: hkallweit1@xxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux- > > > tegra@xxxxxxxxxxxxxxx; Narayan Reddy <narayanr@xxxxxxxxxx> > > > Subject: Re: [PATCH] net: phy: Enhance fixed PHY to support 10G and 5G > > > > > > External email: Use caution opening links or attachments > > > > > > > > > On Wed, Jun 21, 2023 at 10:28:53PM +0530, Revanth Kumar Uppala wrote: > > > > Add 10G and 5G speed entries for fixed PHY framework.These are needed > > > > for the platforms which doesn't have a PHY driver. > > > > > > > > Signed-off-by: Revanth Kumar Uppala <ruppala@xxxxxxxxxx> > > > > Signed-off-by: Narayan Reddy <narayanr@xxxxxxxxxx> > > > > > > This is the second time you have sent me this patch. You have failed to answer > > > the questions i asked you the last time..... > > Apologies for sending twice. > > C45 registers are not defined in the kernel as of now. But, we need to display the speed as 5G/10G when the same is configured as fixed link in DT node. > > It will be great if you can share any data for handling this. > > As of now, with this change we have taken care of providing proper speed log in kernel when 5G/10G is added as fixed links in DT node. > > This is architecturally wrong. As i said, swphy emulates a C22 PHY, > and a C22 PHY does not support speeds greater than 1G. To make swphy > really support 5G and 10G, you would need to add C45 support, and then > extend the default genphy driver to look at the C45 registers as well. > > However, that is all pointless. As i said, phylink fixed-link is not > limited to 1G speeds. Given what i see in Cc: i assume this is for a > tegre SoC? And that uses a Synopsys MAC? So you probably want to > modify the dwc driver to use phylink. Absolutely correct. I seem to recall having had this come up before, and I think it was explained at the time, but I don't seem to find anything in my "sent" mailboxes for the start of 2022 to present. (To nvidia) The classical swphy/fixed-phy offers a software emulated clause 22 PHY so that phylib can be re-used to make a fixed link work without needing special code paths in phylib nor in MAC drivers. However, clause 22 PHYs do not support speeds in excess of 1G, so this places a hard ceiling on the speed that can be supported with this method. PHYLIB's clause 45 support is specific to vendor PHYs, and the "generic" implementation only supports 10G speed. Emulating a specific vendor PHY to achieve this old way of supporting fixed links when we have a better way is really a waste of effort. The "better way" is phylink, which makes fixed links work without needing to resort to PHY emulation, and thus it can support any speed that a MAC happens to support. This is the modern way. We (the phylib and phylink maintainers) will not entertain extending the old now legacy method using swphy/fixed-phy for fixed links to include any faster speeds. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
