linux-kernel - Re: [RFC PATCH] x86: Add safe_udelay() and safe

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Date:	Fri, 14 Jan 2011 00:31:36 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Greg KH <greg@...ah.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()

On Thu, 13 Jan 2011, Yinghai Lu wrote:

> > 
> > What the hell is the root problem ?
> 
> for patch
> 
> x86: usb handoff in early_quirk
> 
> some systems keep getting
>   APIC calibration not consistent with PM-Timer: 139ms instead of 100ms
>   APIC delta adjusted to PM-Timer: 831249 (1163736)
> 
> USB legacy SMI handler is not disabled at that time.
> 
> According to Thomas:
> | http://lkml.indiana.edu/hypermail/linux/kernel/0703.2/0420.html
> | 
> | The wrong calibration values are probably caused by SMM code trying to
> | emulate a PS/2 keyboard from a (maybe connected or not) USB keyboard.
> | This prohibits the accurate delivery of PIT interrupts, which are used
> | to calibrate the local APIC timer. Unfortunately we have no way to
> | disable this BIOS misfeature in the early boot process.
> 
> Try to disable USB legacy support early with this patch.
> So later APIC Timer calibration don't get messed up by USB legacy support SMI handler.
> After this patch, that warning never show up for 100 reboot tests.
> 
> reuse code from drivers/usb/host/pci-quirks.c
> 
> 
> but pci-quirks.c is using udelay and msleep ...
> 
> And BenH does't want 
> 1. if (early)...
> 2. include .c
> 3. new API new about safe_udelay/safe_msleep...
> 
> just want to keep the old udelay/mdelay.

NAK. That's the total wrong thing to do.

Do we have any indication that we miscalibrate? If no, then were is
the point of this ? If yes, then I it's way easier to fix that than
doing all this ugly churn.

We deal with that SMI crap in the TSC calibration as well and I'd
rather see a combined TSC/APIC calibration than all this fugliness.

Thanks,

	tglx
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