mmc: core: Add sysfs entries for dynamic control of clock scaling

Add sysfs attributes to allow dynamic control of clock scaling
parameters. These attributes are used to enable/disable clock
scaling at runtime and change the up_threshold, down_threshold,
and polling_interval values. Complete documentation for these
sysfs entries are provided at "Documentation/mmc/mmc-dev-attrs.txt".

Change-Id: I4753c75c3b3eeea91e93bceba7af2535b793612e
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
mmc: core: claim mmc host while enabling clock scaling from userspace

A race condition can occur while enabling clock scaling and removal
of the card. If the card is removed just after the host->card check
is successful then there could be NULL pointer dereference later.
Claim mmc host before card availability check to avoid this race
condition.

Change-Id: I6339cad5857732ec6b66280940cd6b8b7ed30614
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
mmc: core: run clock scaling only in valid card state

Clock scaling requires the tuning and if the tuning command
is sent to the card in invalid state, tuning procedure will
fail.

With urgent request mechanism implemented, there is a chance
that clock scaling invoked when card is not in a proper state
to receive the tuning command.

This change checks the card state (by sending the status command)
before invoking the clock scaling request.

Change-Id: Icb71a8e74a9afdc70380a5901cd3d28931959e9c
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
mmc: core: Log MMC clock frequency transitions

Use kernel's ftrace support to capture MMC clock frequency
transitions which can be useful for debugging issues related
to power consumption.

Usage:
mount -t debugfs none /sys/kernel/debug
echo 1 > /sys/kernel/debug/tracing/events/mmc/mmc_clk/enable
cat /sys/kernel/debug/tracing/trace_pipe

Change-Id: I25c4ee39dcbe30e7665902a9f723a5a421b55ca3
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>

Conflicts:

	include/trace/events/mmc.h