Re: [PATCH] libata: warn if speed limited due to 40-wire cable (v2)

[Bill Davidsen]

Stephen Clark wrote:
> Bill Davidsen wrote:
>
> > Stephen Clark wrote:
> >  
> >
> > > Bill Davidsen wrote:
> > >
> > >   
> > > > Alan Cox wrote:
> > > >
> > > >
> > > >     
> > > > > > it seems broken to manipulate xfer_mask after returning from the 
> > > > > > driver's ->mode_filter hook.
> > > > > >
> > > > > > this patch is more than just a speed-limited warning printk, afaics
> > > > > >            
> > > > > I actually suggested that order because the only way the printk 
> > > > > can be
> > > > > done correctly is for it to be the very last test made. Since the 
> > > > > mode
> > > > > filter is not told what mode will be used but just subtracts modes 
> > > > > that
> > > > > are not allowed this should be safe.
> > > > >  
> > > > >       
> > > > Far better to have a drive which works slowly than one which works 
> > > > unreliably.
> > > >
> > > >
> > > >
> > > >     
> > > That would be true if the 40 wire detection was 100% accurate!
> > >   
> > The statement is completely correct, even though the detection may 
> > not be. ;-)
> >
> > With the current set(s) of patches to do better detection, cable 
> > evaluation should be better. But even if not, a slow system is more 
> > useful than one which doesn't work, crashes because of swap i/o 
> > errors, etc.
> >
> >  
> I have had problems with cable detection on my previous laptop and my 
> current laptop. It almost made
> my systems unusable. On my current laptop I was getting a thruput of a 
> little over 1 mbps instead
> of the 44 mbps I get with udma set to the correct value. It took hours 
> to upgrade my laptop from
> fc5 to fc6 because of this mis detection.
As far as I can see, if you are getting that low a speed, you have other 
problems. I have a system with old slow drives which are really on a 40 
pin cable, and they run at UDMA(33). One of the experts in this can 
undoubtedly tell us more, but your system should run faster than that, 
mine does, and I really HAVE a 40 pin cable (and drive).

If your system drops to PIO modes, I doubt cable is the only issue, I 
think there are other issues (acpi comes to mind).

--
bill davidsen <davidsen@xxxxxxx>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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