On Thu, Sep 23, 2021 at 6:19 PM Geert Uytterhoeven [off-list ref] wrote:

On Thu, Sep 23, 2021 at 3:42 PM Lee Jones [off-list ref] wrote:

quoted

On Thu, 23 Sep 2021, Krzysztof Kozlowski wrote:

quoted

On 23/09/2021 14:39, Lee Jones wrote:

quoted

As I've explained before, the trigger for all of this was
SERIAL_SAMSUNG which is required for early console on supported
Samsung platforms i.e. this symbol *has* to be built-in.

Actually SERIAL_SAMSUNG does not have to be built-in. It is necessary
for built-in only for debugging or development, not for real products.

Right.  And in the early stages, GKI is used for early (non-released)
H/W (this is also the part of the reason these differences can't be
upstreamed early/now/yet) and sometimes changes break things requiring
low-level debugging techniques to solve (inc. early console).

quoted

Unlike other drivers which have to be built-in, e.g. clocks or pinctrl,
or heavily tested whether setup from initrd works. Plus not breaking
distros who like to have everything as module (solution from Geert?)...

We don't know which drivers *need* to be built-in yet.

Clocks is probably not a good example even, since the power-on default
is most likely all-on, which is fine.  Pinctrl remains to be seen.

Clocks is an excellent example: if a clock is missing, the driver
will fail to probe (unless the clock is considered optional by
the driver), regardless of the power-on or boot loader defaults.
With fw_devlinks=on (which is the default now, and developed by a
Google engineer (GKI or another division?)), the driver won't even
get to the probing point.

Pinctrl is different, as unless I'm mistaken, drivers will still
probe if the pin control driver is missing, so they will work if the
power-on or boot loader defaults of pin control are fine.

In addition, relying on implicit power-on or boot loader state comes
with its own set of pitfalls, which may break other use cases.
On a heavily power-managed mobile device, clocks and/or power domains
can be turned off, so a kernel launched from kexec or kdump may start
in a state not adhering to these implicit dependencies.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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