Re: Calibration issues with USB disc present.

[George Anzinger <george@mvista.com>]

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?

-- 
George Anzinger   george@mvista.com
HRT (High-res-timers):  http://sourceforge.net/projects/high-res-timers/