Re: [PATCH v7 2/2] arm64: boot: Support Flat Image Tree

Hi Ahmad,

On Wed, 29 Nov 2023 at 11:59, Ahmad Fatoum [off-list ref] wrote:

Hi,

a few more comments after decompiling the FIT image:

On 29.11.23 18:21, Simon Glass wrote:

quoted

+    with fsw.add_node('kernel'):
+        fsw.property_string('description', args.name)
+        fsw.property_string('type', 'kernel_noload')

The specification only says no loading done, but doesn't explain what it
means for a bootloader to _not_ load an image. Looking into the U-Boot commit
b9b50e89d317 ("image: Implement IH_TYPE_KERNEL_NOLOAD") that introduces this,
apparently no loading means ignoring load and entry address?

I presume missing load and entry is something older U-Boot versions
were unhappy about? Please let me know if the semantics are as I understood,
so I can prepare a barebox patch supporting it.

Oh, see my previous email.

quoted

+        fsw.property_string('arch', args.arch)
+        fsw.property_string('os', args.os)
+        fsw.property_string('compression', args.compress)
+        fsw.property('data', data)
+        fsw.property_u32('load', 0)
+        fsw.property_u32('entry', 0)
+
+
+def finish_fit(fsw, entries):
+    """Finish the FIT ready for use
+
+    Writes the /configurations node and subnodes
+
+    Args:
+        fsw (libfdt.FdtSw): Object to use for writing
+        entries (list of tuple): List of configurations:
+            str: Description of model
+            str: Compatible stringlist
+    """
+    fsw.end_node()
+    seq = 0
+    with fsw.add_node('configurations'):
+        for model, compat in entries:
+            seq += 1
+            with fsw.add_node(f'conf-{seq}'):
+                fsw.property('compatible', bytes(compat))

The specification says that this is the root U-Boot compatible,
which I presume to mean the top-level compatible, which makes sense to me.

The code here though adds all compatible strings from the device tree though,
is this intended?

Yes, since it saves needing to read in each DT just to get the
compatible stringlist.

quoted

+        fsw.property_string('description', model)
+        fsw.property_string('type', 'flat_dt')
+        fsw.property_string('arch', arch)
+        fsw.property_string('compression', compress)
+        fsw.property('compatible', bytes(compat))

I think I've never seen a compatible for a fdt node before.
What use does this serve?

It indicates the machine that the DT is for.

Regards,
Simon

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