On 07/21/2017 03:51 PM, icenowy@xxxxxxx wrote:
在 2017-07-21 21:02，Andre Przywara 写道：
Hi,
On 21/07/17 13:49, Icenowy Zheng wrote:
于 2017年7月21日 GMT+08:00 下午8:45:39, Andre Przywara
<andre.przywara@xxxxxxx> 写到:
Hi,
On 19/07/17 17:10, Icenowy Zheng wrote:
The Pine64 DT used to contain a dummy vcc3v3 regulator, in order to
satisfy some device nodes when proper AXP803 regulator support is
available. It's in fact the DCDC1 regulator of AXP803.
Drop the dummy regulator, and fix the reference of this regulator to
DCDC1.
Do we really need to have this?
While I see that this is technically correct, it breaks older kernels,
which miss the AXP driver. So we can't use this DT for syncing it into
U-Boot anymore, while still expecting various kernels (for instance
from
distribution installers) to work via UEFI (for which U-Boot provides
the
DT). That would be a shame, because we start to see generic arm64
distribution installers to work out of the box.
I see these solutions:
1) We drop this patch, instead add a comment that technically it's
DCDC1. I believe we can't really turn off DCDC1 anyway.
2) We keep theses patches, but don't sync them to U-Boot to have a
universal DT in there which works with every kernel.
3) We keep these patches *and* sync them to U-Boot, but add the fixed
regulator back in via a U-Boot specific .dtsi "overlay" snippet. This
would take care of the parts that break compatibility. The end result
would be similar to 2), then.
The easiest and most maintainable would be 1), but I am OK with 3) as
well, though I am not sure this won't get messy in the future and will
work for every change that we make.
What do you think?
4) Do nothing.
We only promise old DTs will run with newer kernel, but
we don't promise newer DTs to run with old kernel.And
U-Boot is intended to update less frequently than Linux.
When updateing U-Boot, please update kernel as well.
Which means you tie your firmware to a kernel. I know this is the old
embedded approach, but we should really get rid of this, as I don't see
how this will work nicely with the Pinebook, for instance (which is not
really "embedded" anymore).
U-Boot sits on the SPI flash there, and you are expected to just run any
(not only Linux) distribution from a USB pen drive, for instance, with
that one firmware version, using UEFI. This already works today, but is
only sustainable if we have forward DT compatibility as well.
Old firmware suit both old and new kernels, and for newer firmwares,
use newer kernels.
Congratulations, you basically just broke any Linux distribution out
there :).
This is an intended behavior, and will exist not only on ARM if the
firmware gains something new.
For new features it's some times required to update to new kernels. Once
a platform is out in the market, that should really get limited to
drivers though.
Alex
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