Greg KH wrote:
On Sat, Nov 12, 2005 at 08:06:37AM -0800, George Anzinger wrote:
Greg KH wrote:
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.
Ah... are you saying that the USB support code stops the SMM/SMI prior to
the TSC & delay calibration? Also, this problem was noted in a 2.4.20
kernel. Any help there?
I do not know where in the boot process the TSC and delay calibration is
done. If it happens before the PCI bus is probed, then no, it does not
happen before this.
My guess is that the PCI bus code would like to use delay() so I rather think it is calibrated prior
to this :(
On these boxes, I'd just recommend disabling USB legacy support
completly, if possible. And then complain loudly to the vendor to fix
their BIOS.
But if one is booting from that device...
--
George Anzinger [email protected]
HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/
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