Re: Calibration issues with USB disc present.

[Greg KH <greg@kroah.com>]

On Fri, Nov 11, 2005 at 01:57:07PM -0800, john stultz wrote:
> On Fri, 2005-11-11 at 13:37 -0800, George Anzinger wrote:
> > John,
> > 
> > Have you run into this.  One of the USB disc controllers has the ability to boot the system, 
> > however, it needs SMM code to do this.  This SMM code, somehow, causes SMI interrupts (which are 
> > higher priority than NMI interrutps and not maskable) which it needs to do its thing.
> > 
> > Problem is that if one of these occurs while calibrating the TSC or the delay code, it can cause a 
> > wrong result.  We have seen both a too long and a too short result (depending on where the interrut 
> > happens).
> > 
> > They have found the root cause of TSC calibration problem.
> > Now they ask for the fix or workaround.
> > 
> > That is the BIOS is periodically interrupted by USB controller and the CPU
> > waits during the processing of these interrupts.
> > Their experiments say the interrupt interval is 260mSec and the BIOS needs
> > 150uSec - 200uSec for processing.
> > It is proved that the problem doesn't reproduce by masking such SMI in BIOS.
> > They say SMI is for BIOS emulation for connecting legacy devices to USB.
> > Without such an emulation it's impossible to boot from USB-FD for instance,
> > they say too.
> 
> Hmmm. I haven't heard of this issue specifically, but yes, I'm quite
> familiar with the pain BIOS SMIs can cause and I'm not surprised that it
> would affect the TSC/delay calibration code.
> 
> Is this still an issue w/ 2.6.14? I know the new TSC based delay
> calibration code is supposed to be SMI resilient, but I haven't really
> played with it closely.
> 
> Not sure what the best method to move forward would be. I suspect
> disabling the SMI code early in boot (I thought the usb legacy handoff
> stuff already did this?) would help. Then the actual Linux USB drivers
> can take over before we switch from the initrd to the root filesystem.
> 
> Greg, do you have a suggestion?

I only ever saw this when people forgot to load the USB drivers.  Once
the kernel took over USB support, there was no problem (if there was,
that's a BIOS bug.)  The handoff code in 2.6.14 should help a lot with
this too.

thanks,

greg k-h
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