[U-Boot] [PATCH v3 13/20] Revert: arm64: allwinner: a64: pine64: Use dcdc1 regulator for mmc0

[Emmanuel Vadot]

On Fri, 2 Mar 2018 16:24:22 +0000
Andre Przywara <andre.przywara at arm.com> wrote:

> Hi,
> 
> On 02/03/18 15:58, Maxime Ripard wrote:
> > On Fri, Mar 02, 2018 at 12:56:52AM +0000, Andre Przywara wrote:
> >> Linux kernels before 4.12-rc1 don't know about the AXP803 PMIC, so can't
> >> enable the MMC driver with the current DT anymore, because that now
> >> depends on this regulator.
> > 
> > Given that only I2C, USB and MMC were supported at the time, is it
> > really worth it? There's a lot of incentive to move to a newer kernel
> > given the minimal support it had at the time.
> 
> Yeah, this is somewhat true, although serial, USB and MMC are somewhat
> enough if one uses a USB Ethernet or WiFi adapter. And the kernel choice
> might not always a decision of the user (thinking of distributions here).
> But I was actually unsure about this as well, and wanted to hear some
> opinions.
> 
> One thing that comes to mind is other OSes. Does anyone know how if for
> instance FreeBSD supports the AXP and its Linux bindings? The whole goal
> of this series is to allow booting OSes with U-Boot's DT copy
> ($fdtcontroladdr), so if this patch would make their life easier, it
> might be worth it.

 Not yet but I started the work a few days ago and we should have a
driver soon.

> Regarding the whole forward/backward compatibility:
> I clearly see the difficulty in coming up with a "perfect" DT from day
> one, especially for badly documented SoCs, where mainlining is driven by
> hobbyists. So I was wondering if we introduce a grace period, where we
> declare the DT "unstable" or "subject to incompatible changes" for some
> releases (not too many). In hindsight we might declare 4.12 the stable
> DT base for the A64, for instance.
> This would allow us to start upstreaming early, with a small feature set
> only (just serial + clocks + pinctrl, as for the H6). Additional
> features (PMIC) might then add small incompatibilities (like this one
> here), until we are reasonably confident about the DT.
> Does that sound useful?
> 
> So I am not insisting on this patch, but wanted to point out the
> problems that those seemingly innocent DT changes create and would be
> happy if we can at least try to avoid them in the future.
> 
> Cheers,
> Andre.
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-- 
Emmanuel Vadot <manu at bidouilliste.com> <manu at freebsd.org>