Re: [GIT PULL 2/3] ARM: dts: samsung: DTS for v5.12

Krzysztof Kozlowski
2021-02-06T15:08:10Z

On Sat, Feb 06, 2021 at 03:35:54PM +0100, Arnd Bergmann wrote:
> On Sat, Feb 6, 2021 at 2:45 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> > On Mon, Jan 25, 2021 at 08:12:39PM +0100, Krzysztof Kozlowski wrote:
> > >
> > > ----------------------------------------------------------------
> > > Samsung DTS ARM changes for v5.12
> > >
> > > 1. Use new compatile to properly configure Exynos5420 USB2 PHY, fixing
> > > it suspend/resume cycle.
> > > 2. Correct Samsung PMIC interrupt trigger levels on multiple boards.
> > > 3. Correct the voltages of Samsung GT-I9100 charger and add top-off
> > > charger.
> > >
> >
> > Hi everyone,
> >
> > Any progress or new comments about this pull request?
>
> Hi Krzysztof,
>
> Sorry for not getting back to you on this earlier. I discussed this with
> Olof the other day and we decided to merge this, I just haven't
> gone through the pull requests over the past few days. My plan is
> to do the next round on Monday.
>
> That said, I'm still not happy about the patch we discussed in the
> other email thread[1] and I'd like to handle it a little more strictly in
> the future, but I agree this wasn't obvious and we have been rather
> inconsistent about it in the past, with some platform maintainers
> handling it way more strictly than others.

Thank you for explanation. I would love to receive kind of guidance,
best practices, guide for future patches. I will them write it down and
try to follow during my review. However it made me a sad that a patch,
adhering in my mind to all rules, was postponing the pull request.

>
> I've added the devicetree maintainers and a few other platform
> maintainers to Cc here, maybe they can provide some further
> opinions on the topic so we can come to an approach that
> works for everyone.
>
> My summary of the thread in [1] is there was a driver bug that
> required a DT binding change. Krzysztof and the other involved
> parties made sure the driver handles it in a backward-compatible
> way (an old dtb file will still run into the bug but keep working
> with new kernels), but decided that they did not need to worry
> about the opposite case (running an old kernel with an updated
> dtb). I noticed the compatibility break and said that I would
> prefer this to be done in a way that is compatible both ways,
> or at the minimum be alerted about the binding break in the
> pull request, with an explanation about why this had to be done,
> even when we don't think anyone is going to be affected.
>
> What do others think about this? Should we generally assume
> that breaking old kernels with new dtbs is acceptable, or should
> we try to avoid it if possible, the same way we try to avoid
> breaking new kernels with old dtbs? Should this be a platform
> specific policy or should we try to handle all platforms the same
> way?

Good summary, thanks Arnd. I would like to add that the discussed change
was bringing a new compatible. It was saying: hey, this hardware so far we
treated as old one, but it's not, sorry, it is different, so here you
have a new compatible with a change in few properties as well (and new
bindings which appeared a release earlier).

Best regards,
Krzysztof

>
> Arnd
>
> [1] https://lore.kernel.org/lkml/20210130143949.aamac2724esupt7v@kozik-lap/