[coreboot] flashrom: Cache probed id:s

Peter Stuge peter at stuge.se
Tue Jun 24 06:38:25 CEST 2008

On Tue, Jun 24, 2008 at 04:51:00AM +0200, Carl-Daniel Hailfinger wrote:
> > Best case it is merely pointless to repeat a probe sequence.
> > Worst case it causes system instability, as we saw with the AMIC A49LF040A.
> This problem is not fixed by this patch.

No, but it is one step closer to well-defined, developer-friendly
behavior. The next step is to add a simple list with probe functions,
and execute each one exactly once before the list of flash chips is
even considered.

That way there is a single, simple, definition of the order in which
probes happen, regardless of the order of entries in flashchips.c,
which I very much like having sorted alphabetically.

> > This also shortens flashrom's execution time roughly one second.
> >
> > Signed-off-by: Peter Stuge <peter at stuge.se>
> NACK. This patch randomly (depending on flashchips.c order) breaks
> probing for ~80% of the chips we currently support. If it works for
> you. you are just lucky.

Can you expand on why this would happen?

Keep in mind that each probe function always executes the same code,
no matter which chip is being probed for.

Each probe function implements a particular hardware communication
sequence to read some ID from chip. The function then compares that
ID (same ID every call) to the parameters specified by the caller
(different ID every call) and returns true if they match. My patch
optimizes away the hardware communication for all probe function
calls except the very first one. The ID can not change between calls,
because the hardware communication sequence is identical.

If the ID read from hardware _did_ change between calls (as was the
case in a report to flashrom@ when the delay in probe_jedec() was too
short, before the 2ms patch) that particular probe function is not
working correctly.

If you are fiddling with flash chips electrically on the bus so that
there is actually a different chip connected, I think it is very
reasonable to require flashrom to be rerun.


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