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Re: Install on Orange Pi Plus eMMC work but no reboot

[Removed bug #812611 from the CC list as this mail covers only
 H3/A64-specific information]

On Thu, Oct 06, 2016 at 10:37:19PM +0200, Jean-Christian de Rivaz wrote:
> Le 06. 10. 16 à 21:29, Vagrant Cascadian a écrit :
> >While the SD card images can be used for recovery in many
> >cases, it is also possible that u-boot installed to eMMC fails
> >in such a way that it doesn't fall back to SD card, requiring
> >a lot of effort to reset the board.  It depends entirely on
> >the boot ROM of the board what order it searches for the
> >bootloader...
> Not on that board. The H3 processor chip integrate a boot ROM that
> always first look at the SD card and then at the eMMC (unless
> forced into the special FEL mode).  There is no way to break the
> ROM integrated into the processor chip.  Take a look at
> http://linux-sunxi.org/BROM for the details.

Are you sure about the H3 in this respect? I am not familiar with the
specifics of the H3 and I don't know its exact boot order, so I have
tried to look this information up on https://linux-sunxi.org/BROM. 
Unfortunately this page doesn't seem to contain boot order
information for the H3, only for A10/A20, A31 and A64.

As the A64 looks largely like an H3 that had the A7 cores replaced by
A53 cores, it appears at least possible that the boot process on the
H3 is similar to the one on the A64.

According to https://linux-sunxi.org/BROM, on the A64 SMHC2 (which is
the controller usually used for eMMC as it is the only one that
supports specific faster/wider eMMC-only transfer modes) is the
primary boot target, which means that a broken u-boot with a valid
eGON boot header on the eMMC would hinder the system from dropping
through to SMHC0 which usually drives the SD card socket.  If the
system has a FEL-mode button, it would still be possible to force the
system to FEL mode and perform a recovery operation via FEL, but
without a FEL mode button, the system would be effectively bricked in
such a situation.

Even if the H3 should have two identical bootable MMC controllers,
there is still the question to which one the eMMC and to which one
the SD slot is wired on a specific board.  That might well be
different from board to board depending on the board layout, so it
might theoretically happen that eMMC ends up first in the boot order. 
As long as there is no valid eGON boot header, the system will of
course fall through to the secondary boot option, but if there is a
valid header but wrong code afterwards, the situation could end up
like described above for the A64.

So the boot order might not be problematic on the Orange Pi Plus, but
it can definitely be problematic on A64-based systems and it might
possibly be problematic on other H3-based boards.

This of course doesn't mean that an option to install u-boot to eMMC
from inside the installer isn't useful, just that this needs proper
planning and also probably a configuration at the board level and not
only at the SoC level.

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