arm: tegra: apalis-tk1 and ext clock loopback

Quoted 48 lines · Marcel Ziswiler

Hi Alexander

Quoted 36 lines · Alexander Graf

Quoted 34 lines · Marcel Ziswiler

Hi Alex

Quoted 30 lines · Alexander Graf

Quoted 10 lines · Marcel Ziswiler

This series adds support for the Toradex Apalis TK1 and introduces
a new
option to disable the external clock loopback on SDMMC3.

The whole series is also available here:

http://git.toradex.com/cgit/u-boot-toradex.git/log/?h=for-n
ext

Quoted 16 lines

Changes in v4:
- Re-based.
- Drop patches 2 and 3:
    mmc: tegra: move CONFIG_TEGRA_MMC from headers to defconfigs
    mmc: tegra: introduce CONFIG_TEGRA_MMC to Kconfig in favor of commit 1d2c0506d31a9997e5ffc22e90942902f673b107
    mmc: move more driver config options to Kconfig from Masahiro.
- Meld patch 6
    apalis-tk1: clean-up defconfig
  into first one.
- Add distro boot fallback.
- Enable FIT and device tree overlay support.
- Explicitly drop EFI loader support.

Any particular reason for this?

Quoted 8 lines

Quoted 6 lines

Yes, a waste of 20K which on some of our modules is rather crucial.
I
personally think force enabling EFI for everything was not too smart an
idea but whatever.

Well, it's enabled by default for a good reason: Compatibility.

Quoted 7 lines

While I do agree about compatibility I don't quite see what this has to
do with EFI. I personally don't believe the BIOS/EFI disaster of the
x86 world is worth copying to ARM, sorry. Other distributions like Fedora e.g. achieve the same with distro boot isn't it? After all isn't

Fedora uses extlinux for 32bit ARM and UEFI for 64bit ARM. The main reason they're using extlinux is that at the point in time when they standardized on it as their preferred booting method, the UEFI implementation didn't exist yet.

Quoted 2 lines

the device tree the agreed upon hardware description in the ARM world?

Yes, device tree is very much agree upon as hardware description! And
with UEFI nothing changes in that regard. We still use device tree by
default and unless you're really into shooting yourself into your own
feet I don't see why you'd want to do it any differently.

This is not an ACPI vs DT discussion. It's really just about the question which entity controls selection and handover into the kernel.

With UEFI it's much easier to implement snapshot booting for example,
because you can move all of that logic into a platform agnostic piece of
code. It's the only supported way to have KASLR work on arm64. It allows
for boot selection logic (A/B fallback for example) in something outside
of a boot script or your boot loader sources, so that code stays reusable.

Take a look at my video at ELC for some rationale behind it:

   https://www.youtube.com/watch?v=qJAkJ3nmWgM

Quoted 8 lines

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I want to move to a world where people can just take a random distribution and expect it to work, rather than waste weeks over weeks on fiddling around with random BSPs that nobody really wants
only to realize 2 years down the road that their security footprint
is en par with a swiss cheese.

Quoted 10 lines

Hey, nothing against Swiss cheese! And BTW the term Swiss cheese is about as nonsense as the term Linux. There is really a huge collection
of different Swiss cheeses... Sorry, I just do get upset at times if
certain countries gastronomy people do ask whether I want my sandwich
with Swiss cheese wondering what they mean by that. But I guess those
chaps now do have their very own issues (;-p).

:)

Quoted 22 lines

Quoted 22 lines

It's also the preferred option to boot BSD for example.

So how bad are the 20k for you? In fact, I'm surprised it's 20k at
all -
it used to be 10k. The overhead of DM should be much higher and I doubt
you want to disable that ;). Usually a full U-Boot build is ~500k,
so
even at 20k we're talking about 4% - less than a compiler update usually
gets you.

If size really is such a big concern, moving to THUMB code is going
to
buy you much more in storage savings than dropping (quite useful) UEFI
support.

Quoted 8 lines

Quoted 3 lines

If however there are real technical issues with it, I'm happy to hear
them and fix them as far as possible.

The technical issue is that I still don't quite see why U-Boot needs
EFI. I stopped using SuSE more than 15 years ago and never regretted

For 32bit ARM it doesn't really "need" it. If you feel terribly strongly
about it, I don't have hard feelings with leaving it out. But if it's
really just a matter of taste rather than technical merit, I'd rather
prefer to have the option available for users. The same reason you usually want to have distro boot support enabled and not just a hardcoded bootcmd line.

Quoted 6 lines

it, no pun intended.

But if it is really agreed upon mandatory to enable it I am happy to do
so as I would love to finally get that thing in after an almost 4 months endeavour.

I'm not nacking this patch set, even with EFI_LOADER disabled. But I think that if there's no good reason to disable the feature, we should
leave it enabled.

And if you really are size constrained with today's configuration, please enable thumb2, otherwise you will get bitten on random compiler
updates down the road.

Thanks,

Alex