memory: tegra20-emc: Add devfreq support

Add devfreq support to the Tegra20 EMC driver. Memory utilization
statistics will be periodically polled from the memory controller and
appropriate minimum clock rate will be selected by the devfreq governor.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Link: https://lore.kernel.org/r/20201111011456.7875-5-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

drivers/memory/tegra/Kconfig

@@ -12,7 +12,8 @@ config TEGRA20_EMC
 	tristate "NVIDIA Tegra20 External Memory Controller driver"
 	default y
 	depends on TEGRA_MC && ARCH_TEGRA_2x_SOC
-	select PM_OPP
+	select DEVFREQ_GOV_SIMPLE_ONDEMAND
+	select PM_DEVFREQ
 	help
 	  This driver is for the External Memory Controller (EMC) found on
 	  Tegra20 chips. The EMC controls the external DRAM on the board.

drivers/memory/tegra/tegra20-emc.c

@@ -8,6 +8,7 @@
 #include <linux/clk.h>
 #include <linux/clk/tegra.h>
 #include <linux/debugfs.h>
+#include <linux/devfreq.h>
 #include <linux/err.h>
 #include <linux/interconnect-provider.h>
 #include <linux/interrupt.h>
@@ -102,6 +103,10 @@
 
 #define EMC_FBIO_CFG5_DRAM_WIDTH_X16		BIT(4)
 
+#define EMC_PWR_GATHER_CLEAR			(1 << 8)
+#define EMC_PWR_GATHER_DISABLE			(2 << 8)
+#define EMC_PWR_GATHER_ENABLE			(3 << 8)
+
 static const u16 emc_timing_registers[] = {
 	EMC_RC,
 	EMC_RFC,
@@ -157,6 +162,7 @@ struct emc_timing {
 };
 
 enum emc_rate_request_type {
+	EMC_RATE_DEVFREQ,
 	EMC_RATE_DEBUG,
 	EMC_RATE_ICC,
 	EMC_RATE_TYPE_MAX,
@@ -193,6 +199,8 @@ struct tegra_emc {
 
 	/* protect shared rate-change code path */
 	struct mutex rate_lock;
+
+	struct devfreq_simple_ondemand_data ondemand_data;
 };
 
 static irqreturn_t tegra_emc_isr(int irq, void *data)
@@ -1003,6 +1011,87 @@ static int tegra_emc_init_clk(struct tegra_emc *emc)
 	return 0;
 }
 
+static int tegra_emc_devfreq_target(struct device *dev, unsigned long *freq,
+				    u32 flags)
+{
+	struct tegra_emc *emc = dev_get_drvdata(dev);
+	struct dev_pm_opp *opp;
+	unsigned long rate;
+
+	opp = devfreq_recommended_opp(dev, freq, flags);
+	if (IS_ERR(opp)) {
+		dev_err(dev, "failed to find opp for %lu Hz\n", *freq);
+		return PTR_ERR(opp);
+	}
+
+	rate = dev_pm_opp_get_freq(opp);
+	dev_pm_opp_put(opp);
+
+	return emc_set_min_rate(emc, rate, EMC_RATE_DEVFREQ);
+}
+
+static int tegra_emc_devfreq_get_dev_status(struct device *dev,
+					    struct devfreq_dev_status *stat)
+{
+	struct tegra_emc *emc = dev_get_drvdata(dev);
+
+	/* freeze counters */
+	writel_relaxed(EMC_PWR_GATHER_DISABLE, emc->regs + EMC_STAT_CONTROL);
+
+	/*
+	 *  busy_time: number of clocks EMC request was accepted
+	 * total_time: number of clocks PWR_GATHER control was set to ENABLE
+	 */
+	stat->busy_time = readl_relaxed(emc->regs + EMC_STAT_PWR_COUNT);
+	stat->total_time = readl_relaxed(emc->regs + EMC_STAT_PWR_CLOCKS);
+	stat->current_frequency = clk_get_rate(emc->clk);
+
+	/* clear counters and restart */
+	writel_relaxed(EMC_PWR_GATHER_CLEAR, emc->regs + EMC_STAT_CONTROL);
+	writel_relaxed(EMC_PWR_GATHER_ENABLE, emc->regs + EMC_STAT_CONTROL);
+
+	return 0;
+}
+
+static struct devfreq_dev_profile tegra_emc_devfreq_profile = {
+	.polling_ms = 30,
+	.target = tegra_emc_devfreq_target,
+	.get_dev_status = tegra_emc_devfreq_get_dev_status,
+};
+
+static int tegra_emc_devfreq_init(struct tegra_emc *emc)
+{
+	struct devfreq *devfreq;
+
+	/*
+	 * PWR_COUNT is 1/2 of PWR_CLOCKS at max, and thus, the up-threshold
+	 * should be less than 50.  Secondly, multiple active memory clients
+	 * may cause over 20% of lost clock cycles due to stalls caused by
+	 * competing memory accesses.  This means that threshold should be
+	 * set to a less than 30 in order to have a properly working governor.
+	 */
+	emc->ondemand_data.upthreshold = 20;
+
+	/*
+	 * Reset statistic gathers state, select global bandwidth for the
+	 * statistics collection mode and set clocks counter saturation
+	 * limit to maximum.
+	 */
+	writel_relaxed(0x00000000, emc->regs + EMC_STAT_CONTROL);
+	writel_relaxed(0x00000000, emc->regs + EMC_STAT_LLMC_CONTROL);
+	writel_relaxed(0xffffffff, emc->regs + EMC_STAT_PWR_CLOCK_LIMIT);
+
+	devfreq = devm_devfreq_add_device(emc->dev, &tegra_emc_devfreq_profile,
+					  DEVFREQ_GOV_SIMPLE_ONDEMAND,
+					  &emc->ondemand_data);
+	if (IS_ERR(devfreq)) {
+		dev_err(emc->dev, "failed to initialize devfreq: %pe", devfreq);
+		return PTR_ERR(devfreq);
+	}
+
+	return 0;
+}
+
 static int tegra_emc_probe(struct platform_device *pdev)
 {
 	struct device_node *np;
@@ -1058,6 +1147,7 @@ static int tegra_emc_probe(struct platform_device *pdev)
 	tegra_emc_rate_requests_init(emc);
 	tegra_emc_debugfs_init(emc);
 	tegra_emc_interconnect_init(emc);
+	tegra_emc_devfreq_init(emc);
 
 	/*
 	 * Don't allow the kernel module to be unloaded. Unloading adds some