mmc: Add profiling code to measure performance at MMC layers.

Profiling code is added to measure read, write times for
the MMC requests at various MMC layers. Profiling is done
at the MMC queue and at the driver level. This information
can be viewed through a sysfs entry called perf.

Change-Id: I7c65bfe25a1f7774e3a9abf1f9539e690b3718ec
Signed-off-by: Aparna Mallavarapu <aparnam@codeaurora.org>
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
[subhashj@codeaurora.org: fixed trivial merge conflict]
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
[xiaonian@codeaurora.org: fix trivial merge conflict]
Signed-off-by: Xiaonian Wang <xiaonian@codeaurora.org>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index f2eeb38..9116551 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -19,6 +19,14 @@
 	  This is an option for use by developers; most people should
 	  say N here.  This enables MMC core and driver debugging.
 
+config MMC_PERF_PROFILING
+	bool "MMC performance profiling"
+	depends on MMC != n
+	default n
+	help
+	  If you say Y here, support will be added for collecting
+	  performance numbers at the MMC Queue and Host layers.
+
 if MMC
 
 source "drivers/mmc/core/Kconfig"