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>

Documentation/mmc/mmc-dev-attrs.txt

@@ -39,7 +39,7 @@ SD and MMC Device Attributes
 
 All attributes are read-only.
 
-	cid			Card Identifaction Register
+	cid			Card Identification Register
 	csd			Card Specific Data Register
 	scr			SD Card Configuration Register (SD only)
 	date			Manufacturing Date (from CID Register)
@@ -108,3 +108,41 @@ This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
 	clkgate_delay	Tune the clock gating delay with desired value in milliseconds.
 
 echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
+
+SD/MMC/SDIO Clock Scaling Attributes
+====================================
+
+Read and write accesses are provided to following attributes.
+
+	polling_interval	Measured in milliseconds, this attribute
+				defines how often we need to check the card
+				usage and make decisions on frequency scaling.
+
+	up_threshold		This attribute defines what should be the
+				average card usage between the polling
+				interval for the mmc core to make a decision
+				on whether it should increase the frequency.
+				For example when it is set to '35' it means
+				that between the checking intervals the card
+				needs to be on average more than 35% in use to
+				scale up the frequency. The value should be
+				between 0 - 100 so that it can be compared
+				against load percentage.
+
+	down_threshold		Similar to up_threshold, but on lowering the
+				frequency. For example, when it is set to '2'
+				it means that between the checking intervals
+				the card needs to be on average less than 2%
+				in use to scale down the clocks to minimum
+				frequency. The value should be between 0 - 100
+				so that it can be compared against load
+				percentage.
+
+	enable			Enable clock scaling for hosts (and cards)
+				that support ultrahigh speed modes
+				(SDR104, DDR50, HS200).
+
+echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/polling_interval
+echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/up_threshold
+echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/down_threshold
+echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/enable

drivers/mmc/core/host.c

@@ -4,6 +4,7 @@
  *  Copyright (C) 2003 Russell King, All Rights Reserved.
  *  Copyright (C) 2007-2008 Pierre Ossman
  *  Copyright (C) 2010 Linus Walleij
+ *  Copyright (c) 2012, The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -491,6 +492,163 @@ free:
 }
 
 EXPORT_SYMBOL(mmc_alloc_host);
+
+static ssize_t show_enable(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+
+	if (!host)
+		return -EINVAL;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", mmc_can_scale_clk(host));
+}
+
+static ssize_t store_enable(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+	unsigned long value, freq;
+	int retval = -EINVAL;
+
+	if (!host || !host->card || kstrtoul(buf, 0, &value))
+		goto err;
+
+	if (value && !mmc_can_scale_clk(host)) {
+		if (mmc_card_ddr_mode(host->card) ||
+				mmc_card_hs200(host->card) ||
+				mmc_card_uhs(host->card)) {
+			host->caps2 |= MMC_CAP2_CLK_SCALE;
+			mmc_init_clk_scaling(host);
+		}
+
+		if (!mmc_can_scale_clk(host)) {
+			host->caps2 &= ~MMC_CAP2_CLK_SCALE;
+			goto err;
+		}
+	} else if (!value && mmc_can_scale_clk(host)) {
+		host->caps2 &= ~MMC_CAP2_CLK_SCALE;
+		mmc_disable_clk_scaling(host);
+
+		/* Set to max. frequency, since we are disabling */
+		if (host->bus_ops && host->bus_ops->change_bus_speed) {
+			freq = mmc_get_max_frequency(host);
+			if (host->bus_ops->change_bus_speed(host, &freq))
+				goto err;
+		}
+		host->clk_scaling.initialized = false;
+	}
+	return count;
+err:
+	return retval;
+}
+
+static ssize_t show_up_threshold(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+
+	if (!host)
+		return -EINVAL;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", host->clk_scaling.up_threshold);
+}
+
+#define MAX_PERCENTAGE	100
+static ssize_t store_up_threshold(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+	unsigned long value;
+
+	if (!host || kstrtoul(buf, 0, &value) || (value > MAX_PERCENTAGE))
+		return -EINVAL;
+
+	host->clk_scaling.up_threshold = value;
+
+	pr_debug("%s: clkscale_up_thresh set to %lu\n",
+			mmc_hostname(host), value);
+	return count;
+}
+
+static ssize_t show_down_threshold(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+
+	if (!host)
+		return -EINVAL;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n",
+			host->clk_scaling.down_threshold);
+}
+
+static ssize_t store_down_threshold(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+	unsigned long value;
+
+	if (!host || kstrtoul(buf, 0, &value) || (value > MAX_PERCENTAGE))
+		return -EINVAL;
+
+	host->clk_scaling.down_threshold = value;
+
+	pr_debug("%s: clkscale_down_thresh set to %lu\n",
+			mmc_hostname(host), value);
+	return count;
+}
+
+static ssize_t show_polling(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+
+	if (!host)
+		return -EINVAL;
+
+	return snprintf(buf, PAGE_SIZE, "%lu milliseconds\n",
+			host->clk_scaling.polling_delay_ms);
+}
+
+static ssize_t store_polling(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+	unsigned long value;
+
+	if (!host || kstrtoul(buf, 0, &value))
+		return -EINVAL;
+
+	host->clk_scaling.polling_delay_ms = value;
+
+	pr_debug("%s: clkscale_polling_delay_ms set to %lu\n",
+			mmc_hostname(host), value);
+	return count;
+}
+
+DEVICE_ATTR(enable, S_IRUGO | S_IWUSR,
+		show_enable, store_enable);
+DEVICE_ATTR(polling_interval, S_IRUGO | S_IWUSR,
+		show_polling, store_polling);
+DEVICE_ATTR(up_threshold, S_IRUGO | S_IWUSR,
+		show_up_threshold, store_up_threshold);
+DEVICE_ATTR(down_threshold, S_IRUGO | S_IWUSR,
+		show_down_threshold, store_down_threshold);
+
+static struct attribute *clk_scaling_attrs[] = {
+	&dev_attr_enable.attr,
+	&dev_attr_up_threshold.attr,
+	&dev_attr_down_threshold.attr,
+	&dev_attr_polling_interval.attr,
+	NULL,
+};
+
+static struct attribute_group clk_scaling_attr_grp = {
+	.name = "clk_scaling",
+	.attrs = clk_scaling_attrs,
+};
+
 #ifdef CONFIG_MMC_PERF_PROFILING
 static ssize_t
 show_perf(struct device *dev, struct device_attribute *attr, char *buf)
@@ -582,6 +740,11 @@ int mmc_add_host(struct mmc_host *host)
 	host->clk_scaling.down_threshold = 5;
 	host->clk_scaling.polling_delay_ms = 100;
 
+	err = sysfs_create_group(&host->class_dev.kobj, &clk_scaling_attr_grp);
+	if (err)
+		pr_err("%s: failed to create clk scale sysfs group with err %d\n",
+				__func__, err);
+
 	err = sysfs_create_group(&host->parent->kobj, &dev_attr_grp);
 	if (err)
 		pr_err("%s: failed to create sysfs group with err %d\n",
@@ -615,7 +778,7 @@ void mmc_remove_host(struct mmc_host *host)
 	mmc_remove_host_debugfs(host);
 #endif
 	sysfs_remove_group(&host->parent->kobj, &dev_attr_grp);
-
+	sysfs_remove_group(&host->class_dev.kobj, &clk_scaling_attr_grp);
 
 	device_del(&host->class_dev);