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SubjectRe: I2C_PCA_ISA causes boot delays (was re: sis96x compiled in by error: delay of one minute at boot)
Hello Etienne:

* Etienne Lorrain <etienne_lorrain@yahoo.fr> [2006-03-29 11:26:28 +0200]:
> --- "Mark M. Hoffman" <mhoffman@lightlink.com> wrote:
> > > 885c885
> > > < # CONFIG_I2C_PCA_ISA is not set
> > > ---
> > > > CONFIG_I2C_PCA_ISA=y
> >
> > This alone is the cause of the delay. (I have confirmed it by running some
> > similar .configs here.) You almost certainly don't own this specialized
> > piece of hardware. Worse still, that particular driver has no code to detect
> > whether or not the hardware is present. I cc'ed the listed driver author
> > (Ian) just in case this might be corrected... but I guess there is no way
> > to fix it.
> >
> > So the delay is (1) an I2C bus driver that is not actually present, trying to
> > probe for (2) seven different sensors chip drivers that certainly aren't present
> > on the nonexistent bus. Timeouts ensue.
> >
> > So unless Ian knows a better way to detect that bus driver... the best I can
> > advise is to *not* build in those drivers for hardware that you do not have.
>
> OK, I know the I2C protocol, and I can imagine a hardware board which does
> not have a way to detect its own presence - or the presence of its own ISA bus.
> What I dislike the most is that, after the driver has taken more than 20
> seconds to probe something it did not find, it did not display anything to
> say "either there is a hardware problem, or you should disable me".

I repeat just once more: the supported method for identifying hwmon/sensors
chips is a Perl script called sensors-detect that is distributed with the
lm-sensors package.

> Are you sure that there isn't any distribution around trying to insert
> _all_ the modules to do hardware detection?

No, because that is not supported. All of the major distributions package
lm-sensors, and AFAIK they all build hwmon/sensors as modules. They don't
insert any of them by default. If a distro was silly enough to blindly
insert them all... then it would take forever to boot and nobody would use
it.

> Note that most I2C driver detect abscence of the hardware in a lot less than
> a second: most of the I2C system is fine.

Feel free to write a patch for drivers/busses/i2c/i2c-pca-isa.c; I don't
have that hardware myself. Otherwise, my final advice is:

Patient: It hurts when I do this.
Doctor: Don't do that.

Regards,

--
Mark M. Hoffman
mhoffman@lightlink.com

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