timer_irq_works() is used to detects the timer IRQs. It calls mdelay(10) to
delay ten ticks and check whether the timer IRQ work or not.

mdelay() depends on the loops_per_jiffy which is set up in
calibrate_delay(), but the delay calibration depends on a working timer
interrupt, which causes a chicken and egg problem.

The correct solution is to set up the interrupt mode and making sure that
the timer interrupt is delivered correctly before invoking calibrate_delay().
That means that mdelay() cannot be used in timer_irq_works(). 

Provide helper functions to make a rough delay estimate which is good enough
to prove that the timer interrupt is working. Either use TSC or a simple
delay loop and assume that 4GHz is the maximum CPU frequency to base the
delay calculation on.
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: yinghai@kernel.org
Cc: bhe@redhat.com
Link: https://lkml.kernel.org/r/1505293975-26005-9-git-send-email-douly.fnst@cn.fujitsu.com