Re: [PATCH 1/3] arm: dts: qcom: apq8064: Use 27MHz PXO clock as DSI PLL reference

[Marijn Suijten]

On 2021-08-30 10:58:09, Bjorn Andersson wrote:
[...]
> > > 
> > > Afaik these devices all boots off a boot.img, which means that it's
> > > unlikely that a new kernel is installed on a device with an older DT.
> > > None of them would boot mainline off the DT that shipped with the
> > > original product.
> > 
> > That was my understanding as well, DT overlays are a "new thing" afaik
> > and most devices (at least all Sony's that I'm working with) use an
> > appended DTB that's always in-sync with the kernel image.
> > 
> 
> I think that with the introduction of DT overlays the system becomes
> more flexible and as such more susceptible for bugs caused by unexpected
> DT versions.

Offtopic: We have some problems with this on newer Sony devices where
the BL indeed tries to overlay this DTBO on the DT, which is usually a
downstream DT not fitting on top of a mainline kernel+appended-DTB.  The
solution is to simply wipe DTBO, and afaik it should be fine to compile
the overlay bits directly inside the appended-DTB anyway.  Leads to
unsuspecting problems at times, but it is manageable.

> I think in practice the real issues comes when the DTB is delivered
> separately (i.e. not by boot.img) or inbetween two kernel releases where
> the Qualcomm tree might not be in sync with the driver tree.

Dmitry sees this as a problem for msm8974 but I'm not familiar enough
with the board.  I take it this doesn't use appended DTBs then?

> > > As such, if I pick this patch up as a fix for 5.15 you can respin the
> > > other two patches and they can land in 5.16 and I would be surprised if
> > > anyone will run into any issues with it.
> > > 
> > > I.e. I've applied this patch.
> > 
> > Sounds good, I'll leave this patch out from v2.  Should it have a Fixes:
> > tag to get backported too?
> > 
> 
> Sounds good, I added to this:
> 
> Fixes: 6969d1d9c615 ("ARM: dts: qcom-apq8064: Set 'cxo_board' as ref clock of the DSI PHY")

Did the same on the v2 respin since it seems like those patches were
incomplete without the driver change.

> > Since most review seems to be in I'll respin v2 shortly with the
> > addition of the "ref" clock to msm8974, that should probably get the
> > same treatment (added to 5.15 fixes) then we can land this patchset in
> > 5.16 (maybe without .name= fallback if Dmitry is okay with that).
> > 
> 
> Sounds good.

Sent the msm8974 patch separately and re-spun a v2.  I haven't added the
.name="xo" fallback yet while awaiting Dmitry to see if that counts as
enough time for firmware to be delivered between kernel 5.15 and 5.16.

- Marijn