On Tue, 21 Sep 2021, Krzysztof Kozlowski wrote:

On 21/09/2021 10:11, Lee Jones wrote:

quoted

On Tue, 21 Sep 2021, Krzysztof Kozlowski wrote:

quoted

On 20/09/2021 21:03, Will McVicker wrote:

quoted

This patch series tries to address the issue of ARCH_EXYNOS force selecting
a handful of drivers without allowing the vendor to override any of the
default configs. This takes away from the flexibilty of compiling a generic
kernel with exynos kernel modules. For example, it doesn't allow vendors to
modularize these drivers out of the core kernel in order to share a generic
kernel image across multiple devices that require device-specific kernel
modules.

You do not address the issue in these patches. The problem you describe
is that drivers are not modules and you are not changing them into modules.

The wording is unfortunate.  The reason for this change doesn't have
much to do with kernel modules.

Let's go back in time 18 months or so when Greg KH submitted this [0]
patch, which you Acked.  Greg was trying to solve the problem of not
having to enable ARCH_EXYNOS on kernels which are designed to be
platform agnostic (sometimes called Generic Kernels).  For some reason
SERIAL_SAMSUNG is the only symbol with these dependencies, so the
solution seemed simple and straight forward at the time.

However, For sound reasons Geert NACKed the patch.

Quoting from [1] he says:

  "A generic kernel will include Samsung SoC support, hence
  PLAT_SAMSUNG or ARCH_EXYNOS will be enabled."

Yes, it's correct reasoning. There is also one more use-case -
non-upstreamed (out of tree) platform which wants to use Exynos-specific
drivers. Something like was happening with Apple M1 except that it got
upstreamed and we do not care much about out-of-tree.

quoted

However, since the entry for ARCH_EXYNOS *insists* on building-in a
bunch of other symbols (via 'select') which will be unused in most
cases, this is not a currently acceptable approach for many Generic
Kernels due to size constraints.

In the mainline kernel there is no such use case. If you want to have
Exynos-whatever-driver (e.g. SERIAL_SAMSUNG or S3C RTC), you should
select ARCH_EXYNOS because otherwise it does not make any sense. Zero
sense. Such kernel won't work.

It makes sense only if there is some other work, hidden here, where
someone might want to have SERIAL_SAMSUNG or S3C RTC without
ARCH_EXYNOS. Although GKI is not that work because GKI kernel will
select ARCH_EXYNOS. It must select ARCH_EXYNOS if it wants to support
Exynos platforms.

Therefore I expect first to bring this "some other work, hidden here" to
broader audience, so we can review its use case.

AFAIA, there really isn't any GKI specific code.  Everything that can
be upstreamed, is upstreamed.  The delta consists of some vendor
over-rides (implemented using trace events/hooks spread out over the
code-base), lots of function exports (non-upstreamable due to no
upstream user) and some defconfig/fragments.  There really is nothing
else to share/upstream/unhide.

The only thing GKI needs is a little Kconfig flexibility above what is
currently offered.

quoted

What this patch does is migrates those symbols from being 'select'ed
(always built-in with no recourse) to 'default y'.  Where the former
cannot be over-ridden, but the latter can be via a vendor's
defconfig/fragment.

It cannot be overridden by vendor fragment because options are not
visible. You cannot change them.

The patch does nothing in this regard (making them selectable/possible
to disable), which is why I complained.

100% agree.  As I commented in the other patch, this was a good point
that should be addressed 

quoted

I doubt many (any?) of these symbols can be converted to kernel
modules anyway, as they are required very early on in the boot
sequence.

True, some could, some not. Also some platforms are set up via
bootloader, so actually could "survive" till module is loaded from some
initrd.

If these could be turned into modules, that would be even better!

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog

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