[RFC PATCH 1/3] drivers: amba: Updates to component identification for driver matching.

quoted

The architect field defines what the ARCHID field means (the ARCHID
values are specific to each architect), it's not the same as the
implementer field. You need to check both if you want to know what
component driver to use. The correct mask for that is 0xfff0ffff.

This is a fair point - thought at present the peripheral ID matching takes in the
JDEC ID code of the component designer - in the ETM case ARM (though without
a JDEC continuation code check).
Given this field too is specified as "designer not implementer", it seems logically
unlikely that designer != architect.

It might be exactly like that. On the system I'm using right now:

  DEVARCH=0x47714a13  meaning architect=ARM architecture=ETM
  PIDR= <somebody else>

This is not a Cortex core designed by ARM, it's someone else's ARM
compatible core and they designed their own ARM-compatible ETM.
It conforms to the ETM architecture defined by ARM, so they set
DEVARCH to indicate that (architect=ARM), but in the implementer/
designer code in PIDR they put their own JEDEC code.

If you've got DEVARCH, that should be all you need to select the right
driver and then the driver should be able to get everything it needs
from the feature ID regs. It should only need to look at implementer
code / product code as a last resort for errata workarounds or similar
(e.g. if the feature ID regs are known to be incorrect).

If you haven't got DEVARCH, you have to look at implementer code /
product code. So for example if we see a componet with no DEVARCH
but with designer=ARM product=0x961, that's "ARM product 0x961"
i.e. a TMC, and we can write the driver according to the programming
interface described in the manual for that product.

Al

If we did feel the need to alter the match value / mask values - this happens in
the CS driver code, not in this patch - so will need to be addressed there.

Thanks

Mike

quoted

Al
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--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

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