[U-Boot] [RFC] sunxi: Support uploading 'boot.scr' to RAM over USB OTG in FEL mode

[Ian Campbell]

On Wed, 2015-03-04 at 16:18 +0200, Siarhei Siamashka wrote:
> On Tue, 03 Mar 2015 08:31:17 +0000
> Ian Campbell <ijc+uboot at hellion.org.uk> wrote:
> 
> > On Sun, 2015-03-01 at 23:37 +0200, Siarhei Siamashka wrote:
> > > On Fri, 27 Feb 2015 16:39:45 +0000
> > > Ian Campbell <ijc+uboot at hellion.org.uk> wrote:
> > > 
> > > > On Tue, 2015-02-24 at 04:48 +0200, Siarhei Siamashka wrote:
> > > > > In order to fully support booting the whole system over USB OTG
> > > > > without relying on anything else (MMC, SATA, USB sticks, ...), it
> > > > > is possible to upload the 'boot.scr' file to DRAM using the 'fel'
> > > > > tool. But U-Boot still needs to be able to pick it up there before
> > > > > checking any other boot media.
> > > > > 
> > > > > Signed-off-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>
> > > > > ---
> > > > > 
> > > > > The patch might be not the best way to implement this. But it would
> > > > > be great if U-Boot had out of the box support for:
> > > > >     http://linux-sunxi.org/index.php?title=FEL/USBBoot&oldid=13134#Boot_the_whole_system_over_USB_.28u-boot_.2B_kernel_.2B_initramfs.29
> > > > > 
> > > > > One of the bad things about this patch is that the "scriptaddr"
> > > > > variable needs to be hardcoded and protected agaist modifications
> > > > > (if this address is to be used from the SPL).
> > > > 
> > > > Perhaps use a separate dedicated/hardcoded address for the FEL boot
> > > > script to avoid adding unusual semantics to $scriptaddr (which might
> > > > surprise users not using fel)?
> > > 
> > > Making something that is FEL-boot specific and diverges from the normal
> > > configuration is not great. Is there a real practical need for anyone
> > > to override $scriptaddr and the other similar variables in the
> > > environment? If not, marking them as read-only (similar to how the MAC
> > > address is handled) may be a reasonable solution.
> > 
> > I've certainly had to mess with $*addr in order to workaround issues
> > with older versions of Xen booting on the cubietruck.
> 
> Was it really necessary to mess with the environment variables for
> the older versions of Xen? Or just hardcoding some magic addresses
> in the boot.scr could also solve the problem just fine?

I suppose that would have worked, but as a naive user I would have been
very surprised if setenv fooaddr didn't work and probably spent a lot of
time trying to figure out why..

> Could you please tell us more about this old Xen address space
> allocation requirements? Would it be difficult to change the sunxi
> U-Boot defaults to accommodate them?

I think there's no need, the version is now ancient history.

The issue was todo with making a single contiguous allocation for the
first domain, because it needed to be aligned to its size the placement
of the various bits in memory at boot meant that only quite a small
initial domain could be allocated in practice. That's fixed now though.


> 
> > More generally I think diverging from the norm with a sunxi specific
> > variable is preferable to changing the semantics of existing variables
> > to make them r/o, which will make sunxi inconsistent with other u-boot
> > platforms.
> 
> Consistency with the other U-Boot platforms is a valid point.
> 
> > > > If the FEL address has to be 0x43100000 for compatibility with existing
> > > > instructions/tools that might mean moving the current scriptaddr
> > > > elsewhere. I think we can live with that.
> > > 
> > > There was an idea to make mksunxiboot tool store all these magic
> > > addresses into the bootable image, so that the fel tool could find
> > > them there. Some of such ideas are listed here:
> > > 
> > >     http://linux-sunxi.org/FEL/USBBoot#Potential_future_improvements_for_u-boot_v2015.07
> > > 
> > > This can only work if these addresses become compile time constants
> > > and can't be overridden by the environment.
> > 
> > I'm afraid that won't fly, $fooaddr are not r/o variables.
> 
> They are not r/o variables today. But the U-Boot keeps evolving.

If you want to propose making them r/o for all platforms then please do
so, but lets not make sunxi a special case here. (Personally I don't
think it will fly, but you can always ask).

>  For
> example, it got Kconfig support, which offers an alternative to the
> environment to some extent.

Not really, the environment is user tweakable.

> > When felbooting there doesn't seem to be any particular reason why you
> > have to use $fooaddr from the environment, they could just as well be
> > addresses set by the boot.scr itself, whether derived from the eGON
> > header or not.
> 
> We do have the reasons to settle with some good set of addresses,
> which are known to be mostly problem free.

We should of course provide good defaults, but doesn't follow that we
should make it impossible to change them. And, again, if you want to go
this route then it should not be sunxi specific.

> Otherwise people start being creative with assigning addresses and
> run into troubles. For example, I have seen reports from the people
> failing to boot the old sunxi-3.4 kernel just because the initrd was
> clashing with the CMA area reservation.

These people should just use the defaults then.

> > Regardless, the above BOOTENV_DEV type stuff is how the common
> > config_distro_bootcmd.h setup for adding a boot device works and should
> > be used. Or you can try and convince the maintainers it should be done
> > some other way globally, the important thing is that sunxi shouldn't be
> > more special than necessary.
> 
> I don't see why this should be a global change.

This new boot method should be part of config_distro_bootcmd.h.
Therefore it should follow the existing mechanisms for adding a new boot
method. _If_ you object to the existing mechanisms then you should fix
them globally, not do things in some special way for sunxi.

> 
> > > IMHO all the necessary adjustments to the environment variables can
> > > be done at runtime in the misc_init_r() function. For example,
> > > pre-pending "fel" to the "boot_targets" variable can be done based
> > > on a runtime check and activated only for the FEL mode.
> > 
> > This means the user cannot adjust things to suit their local needs,
> > either disabling the fel script support or inserting it into the boot
> > order wherever they want. Hardcoding that stuff in C is not a solution
> > here I'm afraid.
> 
> More like you are suggesting that a user needs to have even more
> reasons to do unwieldy environment maintenance and be able to shoot
> himself in the foot.

The average user will use the default environment and it will just work,
no need to do any environment maintenance.

The ability to changes things is not for the average user.

> Instead of the code deciding what is the right
> thing to do automatically.

The default enviroment should do the right thing automatically, so
people get the right thing be default. Nobody is suggesting otherwise.

> It makes no sense for the user to really adjust things by modifying
> and storing the environment for the purpose of disabling the fel
> script support.

>  We want this fel script support feature precisely
> because we have no other way to modify the environment or deliver
> the information to U-Boot in another (reasonable) way in certain
> configurations (with only the serial console and USB OTG available).
> The other configurations don't need the fel script support feature
> in the first place, so there is nothing to disable there.

They will get the default environment and work as you want and they
expect.

Ian.