Re: Linux 2.4.2ac12 (vt82c686 info)

[Andre Hedrick]

Daniela,

Great to hear from you again my dear! ;-)

On Fri, 9 Mar 2001, Vojtech Pavlik wrote:

> On Fri, Mar 09, 2001 at 08:25:43AM +0100, Daniela Engert wrote:
> 
> > >They're about the same - only Alan didn't like the PCI speed measurement
> > >code that's new in the 4.x series, so I added all the other changes to
> > >the 3.20 driver, and 3.21 was born.
> > 
> > I do understand Alan's objections against this speed measurement code
> > very well. I have similar code built into other (non-Linux) drivers,
> > and according to the many user reports that I got the measurement
> > results should be taken with a grain of salt. It is working perfectly
> > in most cases, but it may fail from time to time. There is a hidden
> > assumption in this type of measurement which the device that you run
> > the test against has to fulfill. If it doesn't (and it is not required
> > to do to be conforming to the ATA spec), the measurement results (PCI
> > bus clock) are bogus (typically way too high).
> 
> Actually I don't think my method can ever result in a measurement higher
> than real PCI clock, but can result in a lower one (if the device
> deasserts IORDY even on a speed slower than PIO_0), which is also a
> problem. Anyway, on fast machines the accuracy of the current algorithm
> is +- .01 MHz.
> 
> Once tested a little more, the measurement will probably go in, however
> with an option for the user to override it with a command line
> parameter.
> 
> Btw, if it isn't a secret - what other drivers are those and what is the
> exact method you used ... ?
> 
> -- 
> Vojtech Pavlik
> SuSE Labs
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Andre Hedrick
Linux ATA Development
ASL Kernel Development
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