Re: [RFC PATCH net] Revert "net: phy: Uniform PHY driver access"

On Tue, Sep 14, 2021 at 12:06:18PM +0000, Vladimir Oltean wrote:

On Mon, Sep 13, 2021 at 08:49:19PM +0200, Andrew Lunn wrote:

quoted

quoted

I am not sure why "to_phy_driver" needs cleanup. Au contraire, I think
the PHY library's usage of struct phy_device :: drv is what is strange
and potentially buggy, it is the only subsystem I know of that keeps its
own driver pointer rather than looking at struct device :: driver.

There is one odd driver in the mix. Take a look at xilinx_gmii2rgmii.c.

It probably could be done a better way, but that is what we have.

Interesting, to say the least. Also, is there any connection between
that and the revert I'm proposing?

If i remember correctly, Gerhard Engleder is actually using this, and
ran into a problem because the wrong driver structure was used.

So compared to other vendors, where the RGMII gasket is part of the MAC
device, with Xilinx Zynq it is accessible via MDIO?

Yes. Its control plane sits on the MDIO bus. Unfortunately, it does
not have any ID registers, so it does not directly appear as a PHY. So
it does interesting things it put itself in the control path to the
real PHY.

It looks like it is said that this GMII2RGMII converter can be placed in
front of any GMII MAC. Nice that there are zero in-tree users of
"xlnx,gmii-to-rgmii-1.0" so that I could figure out exactly how that
plays out in practice.

If you look back at the thread for that patch, i think Gerhard posted
a DT fragment he is using. Hopefully it will get submitted as a full
board description at some point.

Note that the usage of priv->phy_dev, priv->phy_drv, priv->conv_phy_drv
beats me. Why is "phy_dev" kept inside "priv" even though it is accessed
only inside xgmiitorgmii_probe? Why does xgmiitorgmii_configure() need to
be called from xgmiitorgmii_read_status() which in turn hooks into the
attached PHY driver's phy_read_status()? Why does xgmiitorgmii_configure
not get exported and called from an .adjust_link method or the phylink
equivalent, like any other MAC-side hardware linked with the PHY library
in the kernel?

I was never happy with this driver. It got submitted before i went on
vacation, i had a few rounds trying to get the submitter to refactor
it and was mostly ignored. I left on vacation with lots of open review
points, and when i got back it had been merged. And the original
submitters never responded to my requests for improvements.

	Andrew