Re: [PATCH] x86, tsc: Fix tsc ratio calibration to avoid broken mdelay

[Thomas Gleixner]

On Fri, 6 May 2016, Thomas Gleixner wrote:
> On Fri, 6 May 2016, yu.c.chen@xxxxxxxxx wrote:
> > From: Chen Yu <yu.c.chen@xxxxxxxxx>
> > 
> > Currently we fetch the tsc radio by:
> > ratio = (lo >> 8) & 0x1f;
> > thus get bit8~bit12 of the MSR_PLATFORM_INFO, however according
> > to Intel 64 and IA-32 Architectures Software Developer Manual 35.5,
> > the ratio bit should be bit8~bit15, otherwise we might get incorrect
> > tsc ratio and cause system hang later(mdelay corrupted).
> 
> The resulting issue is that both TSC frequency, which is used for udelay, and
> the lapic timer frequency are wrong. mdelay is just the visible damage caused
> by that.

Aside of that:

> Cc: 3.14+ <stable@xxxxxxxxxxxxxxx> # 3.14+

Please use:

Fixes: commit '....'

next time, which identifies the kernel version to which this needs to be
backported and gives a reference to the commit which caused the issue.

Thanks,

	tglx