[GIT PULL] Allwinner Fixes for 5.10

[Ard Biesheuvel]

On Thu, 29 Oct 2020 at 22:41, Arnd Bergmann <arnd at kernel.org> wrote:
>
> On Thu, Oct 29, 2020 at 10:23 PM Arnd Bergmann <arnd at kernel.org> wrote:
> >
> > On Thu, Oct 29, 2020 at 8:06 PM Maxime Ripard <mripard at kernel.org> wrote:
> > >
> > > ----------------------------------------------------------------
> > > Mostly some fixes for a fallout in a PHY driver that pointed out errors
> > > in our DTs.
> >
> > Can you clarify what this means for compatibility of the dtb files?
> >
> > I would assume that the modified .dts files all work on older kernels
> > because you fix the setting, but at least some of them require
> > the patch with newer kernels, right?
> >
> > Are they all broken without the change? Are other platforms
> > likely to suffer the same problem? IIRC seems that at least
> > the SynQuacer box had the same issue, but I don't yet
> > understand how common the problem is.
>
> To clarify: I had pulled the branch already when I replied, but the
> automated email for that apparently did not trigger.
>
> I would like to know the background here mainly so I can put
> it into my pull request to Linus.
>

The Realtek PHY driver used to ignore the TX/RX delay settings implied
by the xxx in the the different rgmii-xxx phy-mode settings, and a
failed attempt was made in the v5.2 timeframe to change this, and so
the -xxx part has been effectively ignored all this time, meaning you
could get away with providing the wrong value.

Even though no platform appears to have been affected by this
incorrect patch, the followup fix that repairs it has been backported
to -stable, breaking all the formerly working platforms incorporating
this PHY that describe the mode as 'rgmii' instead of 'rgmii-id'. I
have argued that the backport of the followup fix should be reverted,
given that there is a risk that production systems tracking a -stable
release may be affected by this if they don't take their DT directly
from the upstream kernel.

I think this PR is fine, though - fixing the DTs going forward is
needed in any case (although I think backporting DT changes to -stable
is a bad idea but that is just my opinion)