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>

drivers/mmc/core/core.c

@@ -1122,6 +1122,19 @@ void mmc_set_ios(struct mmc_host *host)
 	if (ios->clock > 0)
 		mmc_set_ungated(host);
 	host->ops->set_ios(host, ios);
+	if (ios->old_rate != ios->clock) {
+		if (likely(ios->clk_ts)) {
+			char trace_info[80];
+			snprintf(trace_info, 80,
+				"%s: freq_KHz %d --> %d | t = %d",
+				mmc_hostname(host), ios->old_rate / 1000,
+				ios->clock / 1000, jiffies_to_msecs(
+					(long)jiffies - (long)ios->clk_ts));
+			trace_mmc_clk(trace_info);
+		}
+		ios->old_rate = ios->clock;
+		ios->clk_ts = jiffies;
+	}
 }
 EXPORT_SYMBOL(mmc_set_ios);
 

include/linux/mmc/host.h

@@ -23,6 +23,8 @@
 
 struct mmc_ios {
 	unsigned int	clock;			/* clock rate */
+	unsigned int	old_rate;       /* saved clock rate */
+	unsigned long	clk_ts;         /* time stamp of last updated clock */
 	unsigned short	vdd;
 
 /* vdd stores the bit number of the selected voltage range from below. */

include/trace/events/mmc.h

@@ -158,7 +158,25 @@ DEFINE_EVENT(mmc_adma_class, mmc_adma_table_post,
 	TP_PROTO(unsigned int cmd, unsigned int len),
 	TP_ARGS(cmd, len));
 
-#endif /* _TRACE_MMC_H */
+TRACE_EVENT(mmc_clk,
+	TP_PROTO(char *print_info),
+
+	TP_ARGS(print_info),
+
+	TP_STRUCT__entry(
+		__string(print_info, print_info)
+	),
+
+	TP_fast_assign(
+		__assign_str(print_info, print_info);
+	),
+
+	TP_printk("%s",
+		__get_str(print_info)
+	)
+);
+
+#endif /* if !defined(_TRACE_MMC_H) || defined(TRACE_HEADER_MULTI_READ) */
 
 /* This part must be outside protection */
 #include <trace/define_trace.h>