Re: Generic interface for accelerometers (AMS, HDAPS, ...)
From: Robert Hancock
Date: Thu Jul 06 2006 - 21:43:13 EST
Vojtech Pavlik wrote:
HDAPS talks to the embedded controller using IO over the LPC bus, and not
to
the accelerometer chip or to a simple A/D i2c chip which is used excusively
for accelerometer access. The EC interface for HDAPS data retrieval is
not friendly to any errors, and hardlocks the machine somehow if any
firmware bugs hit or if we violate any of the rules (that are not written
anywhere) about how to access the EC without geting the SMBIOS unhappy.
So, turning off HDAPS polling while it is not necessary really looks like a
good idea overall.
We are investigating the ACPI global lock as a way to at least get the
SMBIOS to stay away from the EC while we talk to it, but we don't know if
the entire SMBIOS firmware respects that lock.
It had better, that is exactly what the ACPI Global Lock is supposed to
prevent (concurrent access to non-sharable resources between the OS and
SMI code). The ACPI DSDT contains information on whether or not the
machine requires the Global Lock in order to access the EC or whether it
is safe to access without locking.
Isn't that vaild only if you actully use ACPI to access the EC? (AFAIK
the HDAPS driver does direct port access.)
Likely - and I think you would have to do that anyway, otherwise how are
you going to prevent the ACPI code from concurrently accessing the EC at
the same time as the HDAPS driver? In any case, only ACPI knows how to
safely access the EC (Global Lock needed, or not) so it should be the
one doing the accesses.
--
Robert Hancock Saskatoon, SK, Canada
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Home Page: http://www.roberthancock.com/
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