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The TSC calibration code uses HPET as reference. The conversion normalizes
the delta of two HPET timestamps:
hpetref = ((tshpet1 - tshpet2) * HPET_PERIOD) / 1e6
and then divides the normalized delta of the corresponding TSC timestamps
by the result to calulate the TSC frequency.
tscfreq = ((tstsc1 - tstsc2 ) * 1e6) / hpetref
This uses do_div() which takes an u32 as the divisor, which worked so far
because the HPET frequency was low enough that 'hpetref' never exceeded
32bit.
On Skylake machines the HPET frequency increased so 'hpetref' can exceed
32bit. do_div() truncates the divisor, which causes the calibration to
fail.
Use div64_u64() to avoid the problem.
[ tglx: Fixes whitespace mangled patch and rewrote changelog ]
Signed-off-by: Xiaoming Gao <newtongao@tencent.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Cc: peterz@infradead.org
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/38894564-4fc9-b8ec-353f-de702839e44e@gmail.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.