netdev - Re: realtek PHY commit bbc4d71d63549 causes regression

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Date:   Thu, 29 Oct 2020 16:21:00 +0200
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steve McIntyre <steve@...val.com>,
        "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
        <netdev@...r.kernel.org>, Willy Liu <willy.liu@...ltek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Masahisa Kojima <masahisa.kojima@...aro.org>
Subject: Re: realtek PHY commit bbc4d71d63549 causes regression

Hi Andrew

On Sun, Oct 25, 2020 at 03:42:58PM +0100, Andrew Lunn wrote:
> On Sun, Oct 25, 2020 at 03:34:06PM +0100, Ard Biesheuvel wrote:
> > On Sun, 25 Oct 2020 at 15:29, Andrew Lunn <andrew@...n.ch> wrote:
> > >
> > > On Sun, Oct 25, 2020 at 03:16:36PM +0100, Ard Biesheuvel wrote:
> > > > On Sun, 18 Oct 2020 at 17:45, Andrew Lunn <andrew@...n.ch> wrote:
> > > > >
> > > > > > However, that leaves the question why bbc4d71d63549bcd was backported,
> > > > > > although I understand why the discussion is a bit trickier there. But
> > > > > > if it did not fix a regression, only broken code that never worked in
> > > > > > the first place, I am not convinced it belongs in -stable.
> > > > >
> > > > > Please ask Serge Semin what platform he tested on. I kind of expect it
> > > > > worked for him, in some limited way, enough that it passed his
> > > > > testing.
> > > > >
> > > >
> > > > I'll make a note here that a rather large number of platforms got
> > > > broken by the same fix for the Realtek PHY driver:
> > > >
> > > > https://lore.kernel.org/lkml/?q=bbc4d71d6354
> > > >
> > > > I seriously doubt whether disabling TX/RX delay when it is enabled by
> > > > h/w straps is the right thing to do here.
> > >
> > > The device tree is explicitly asking for rgmii. If it wanted the
> > > hardware left alone, it should of used PHY_INTERFACE_MODE_NA.
> > >
> > 
> > Would you suggest that these DTs remove the phy-mode instead? As I
> > don't see anyone proposing that.
> 
> What is also O.K, for most MAC drivers. Some might enforce it is
> present, in which case, you can set it to "", which will get parsed as
> PHY_INTERFACE_MODE_NA. But a few MAC drivers might configure there MII
> bus depending on the PHY mode, RGMII vs GMII.
> 
>     Andrew

What about reverting the realtek PHY commit from stable?
As Ard said it doesn't really fix anything (usage wise) and causes a bunch of
problems.

If I understand correctly we have 3 options:
1. 'Hack' the  drivers in stable to fix it (and most of those hacks will take 
   a long time to remove)
2. Update DTE of all affected devices, backport it to stable and force users to
update
3. Revert the PHY commit

imho [3] is the least painful solution.


Thanks
/Ilias