[U-Boot] [PATCH 0/5] sunxi: env: Load environment from boot media

[Tom Rini]

On Tue, Jun 11, 2019 at 11:37:28AM +0200, Maxime Ripard wrote:
> On Mon, Jun 10, 2019 at 10:11:39AM +0100, Andre Przywara wrote:
> > On Mon, 10 Jun 2019 10:30:37 +0200
> > Maxime Ripard <maxime.ripard at bootlin.com> wrote:
> >
> > Hi Maxime,
> >
> > thanks for having a look!
> >
> > > On Sat, Jun 08, 2019 at 02:26:53AM +0100, Andre Przywara wrote:
> > > > At the moment we need to configure the place where U-Boot tries to load
> > > > its environment from at compile time. This is not only inflexible, but
> > > > also unnecessary, as we have easy access to the boot source.
> > > >
> > > > This series prepares U-Boot on Allwinner boards to load the environment
> > > > from the same media where the SPL and U-Boot proper were loaded from.
> > > > This allows to keep one firmware binary, and copy it to an SD card,
> > > > eMMC or even SPI flash, without needing to configure it differently.
> > >
> > > This does change a couple of things though. The environment used to be
> > > loaded always from the same source, no matter the boot device. This
> > > means that if you would set an SD card, you would get the environment
> > > from the eMMC. Same thing for FEL. This is no longer the case.
> > >
> > > I don't know whether it's a good or a bad thing, but it should be
> > > mentionned.
> >
> > This is true, I failed to mention that.
> >
> > To start a discussion on this:
> > I consider the current (fixed location) behaviour somewhat surprising and
> > limiting, and couldn't find a real use case where this would be required.
> > Happy to hear of one!
> > Instead I thought about those cases:
> > - There is some botched U-Boot plus environment on the eMMC. You want to
> > boot from SD card to have a clean start, possibly to fix it. But it will
> > load the possibly outdated, broken or even unrelated environment from eMMC.
> 
> This one might be a feature though. Being able to restore / fix an
> environment in the eMMC running from an SD card has save me a couple
> of times. Or booting from the SD card because the U-Boot on the eMMC
> is broken, while the environment is working.
> 
> > - You want to boot from SD card without touching the eMMC at all. Saving
> > the environment will spoil that.
> 
> But it goes against that one, which might be more important / sensible.
> 
> > - You want to have one image for all possible boot media.
> 
> That won't happen, only because NAND is a thing.

Some of this is perhaps an argument for adding a sub-command to specify
where the environment is to be read from.  Heuristics are still only a
best guess and won't get it right every time.

> And even then, I'm not really sure that it's a good thing. A U-Boot
> build these days is roughly in the same sizes than a stripped down
> Linux image. For an inferior solution in pretty much every aspect.

Hey now.  We aren't _quite_ that large.  And we are (really!) trying to
find a happy medium between "distros want X/Y/Z for everyone" and "can
we commonly get back to UNDER 512kB maybe?  Please?".

-- 
Tom
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