Discussion: PNOR image verification (and possibly Virtual PNOR) on 64MiB flash

[Lei YU]

This email is to discuss about PNOR image verification on 64MiB flash, and
possibly it may involve Virtual PNOR feature.

Background:
Witherspoon has 128MiB flash, enables PNOR image verification and Virtual
PNOR
feature, implemented by openpower-software-manager.
And it has the assumptions of:
1. Enough space for 2 PNOR images, thus physically 128MiB flash chip is
   needed;
2. UBIFS on PNOR;
3. PNOR build in squashfs with signatures.

Most OpenPOWER machines uses 64MiB PNOR flash and non-UBIFS, so I would like
to discuss how to support PNOR image verification on smaller chips.

We have two ways:
1. Change to use UBIFS and Virtual PNOR feature with
   openpower-software-manager;
2. Keep current fixed layout, and added new code to support image
   verification.

For 1, it needs code change to assume there is only space for one PNOR
image,
then we get all the exiting features: PNOR version, image sign verification,
code update and virtual PNOR.

For 2, quite a lot of changes are needed:
* Generate signature for the whole pnor image (in op-build);
* Changes in openpower-software-manager to get version of PNOR;
* Changes in openpower-software-manager to support code update of fixed PNOR
   layout;

So I would prefer 1, to make openpower-software-manager support single PNOR
image.

What do you think?
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