[U-Boot] SPL_FIT_SIGNATURE on am3358

13 Feb 2019

      I'm having trouble getting verified boot working in SPL on an am3358 based
platform.
The problem I hit is when fit_image_verify_with_data()
calls fit_image_verify_required_sigs().  The 5th argument (sig_blob) is
gd_fdt_blob() which resolves to NULL.  This argument should be the FDT
containing the public keys.  I assume this happens because SPL_OF_CONTROL
isn't enabled.  As far as I can tell, SPL_OF_CONTROL isn't working on
am33xx boards; enabling it causes SPL to loop infinitely in i2c init (tried
on my custom hardware as well as Beaglebone Black).
So the public key needs to be found elsewhere.  I can keep a separate FDT
with the public key stored in a read-only location.  My question is what is
the 'right' way to load it?  Is there an interface for
populating gd_fdt_blob() with my own FDT (without SPL_OF_CONTROL enabled)?
Or should I modify fit_image_verify_with_data() to get the FDT from
elsewhere (and probably other similar calls as well)?
-Doug
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