memory: tegra: Support DVFS on Tegra186 and later

Add a Tegra186 (and later) EMC driver that reads the EMC DVFS tables
from BPMP and uses the EMC clock to change the external memory clock.

This currently only provides a debugfs interface to show the available
frequencies and set lower and upper limits of the allowed range. This
can be used for testing the various frequencies. The goal is to
eventually integrate this with the interconnect framework so that the
EMC frequency can be scaled based on demand from memory clients.

Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/memory/tegra/Makefile

@@ -13,4 +13,4 @@ obj-$(CONFIG_TEGRA_MC) += tegra-mc.o
 obj-$(CONFIG_TEGRA20_EMC)  += tegra20-emc.o
 obj-$(CONFIG_TEGRA30_EMC)  += tegra30-emc.o
 obj-$(CONFIG_TEGRA124_EMC) += tegra124-emc.o
-obj-$(CONFIG_ARCH_TEGRA_186_SOC) += tegra186.o
+obj-$(CONFIG_ARCH_TEGRA_186_SOC) += tegra186.o tegra186-emc.o

drivers/memory/tegra/tegra186-emc.c

@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2019 NVIDIA CORPORATION.  All rights reserved.
+ */
+
+#include <linux/clk.h>
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+
+#include <soc/tegra/bpmp.h>
+
+struct tegra186_emc_dvfs {
+	unsigned long latency;
+	unsigned long rate;
+};
+
+struct tegra186_emc {
+	struct tegra_bpmp *bpmp;
+	struct device *dev;
+	struct clk *clk;
+
+	struct tegra186_emc_dvfs *dvfs;
+	unsigned int num_dvfs;
+
+	struct {
+		struct dentry *root;
+		unsigned long min_rate;
+		unsigned long max_rate;
+	} debugfs;
+};
+
+/*
+ * debugfs interface
+ *
+ * The memory controller driver exposes some files in debugfs that can be used
+ * to control the EMC frequency. The top-level directory can be found here:
+ *
+ *   /sys/kernel/debug/emc
+ *
+ * It contains the following files:
+ *
+ *   - available_rates: This file contains a list of valid, space-separated
+ *     EMC frequencies.
+ *
+ *   - min_rate: Writing a value to this file sets the given frequency as the
+ *       floor of the permitted range. If this is higher than the currently
+ *       configured EMC frequency, this will cause the frequency to be
+ *       increased so that it stays within the valid range.
+ *
+ *   - max_rate: Similarily to the min_rate file, writing a value to this file
+ *       sets the given frequency as the ceiling of the permitted range. If
+ *       the value is lower than the currently configured EMC frequency, this
+ *       will cause the frequency to be decreased so that it stays within the
+ *       valid range.
+ */
+
+static bool tegra186_emc_validate_rate(struct tegra186_emc *emc,
+				       unsigned long rate)
+{
+	unsigned int i;
+
+	for (i = 0; i < emc->num_dvfs; i++)
+		if (rate == emc->dvfs[i].rate)
+			return true;
+
+	return false;
+}
+
+static int tegra186_emc_debug_available_rates_show(struct seq_file *s,
+						   void *data)
+{
+	struct tegra186_emc *emc = s->private;
+	const char *prefix = "";
+	unsigned int i;
+
+	for (i = 0; i < emc->num_dvfs; i++) {
+		seq_printf(s, "%s%lu", prefix, emc->dvfs[i].rate);
+		prefix = " ";
+	}
+
+	seq_puts(s, "\n");
+
+	return 0;
+}
+
+static int tegra186_emc_debug_available_rates_open(struct inode *inode,
+						   struct file *file)
+{
+	return single_open(file, tegra186_emc_debug_available_rates_show,
+			   inode->i_private);
+}
+
+static const struct file_operations tegra186_emc_debug_available_rates_fops = {
+	.open = tegra186_emc_debug_available_rates_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
+static int tegra186_emc_debug_min_rate_get(void *data, u64 *rate)
+{
+	struct tegra186_emc *emc = data;
+
+	*rate = emc->debugfs.min_rate;
+
+	return 0;
+}
+
+static int tegra186_emc_debug_min_rate_set(void *data, u64 rate)
+{
+	struct tegra186_emc *emc = data;
+	int err;
+
+	if (!tegra186_emc_validate_rate(emc, rate))
+		return -EINVAL;
+
+	err = clk_set_min_rate(emc->clk, rate);
+	if (err < 0)
+		return err;
+
+	emc->debugfs.min_rate = rate;
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(tegra186_emc_debug_min_rate_fops,
+			tegra186_emc_debug_min_rate_get,
+			tegra186_emc_debug_min_rate_set, "%llu\n");
+
+static int tegra186_emc_debug_max_rate_get(void *data, u64 *rate)
+{
+	struct tegra186_emc *emc = data;
+
+	*rate = emc->debugfs.max_rate;
+
+	return 0;
+}
+
+static int tegra186_emc_debug_max_rate_set(void *data, u64 rate)
+{
+	struct tegra186_emc *emc = data;
+	int err;
+
+	if (!tegra186_emc_validate_rate(emc, rate))
+		return -EINVAL;
+
+	err = clk_set_max_rate(emc->clk, rate);
+	if (err < 0)
+		return err;
+
+	emc->debugfs.max_rate = rate;
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(tegra186_emc_debug_max_rate_fops,
+			tegra186_emc_debug_max_rate_get,
+			tegra186_emc_debug_max_rate_set, "%llu\n");
+
+static int tegra186_emc_probe(struct platform_device *pdev)
+{
+	struct mrq_emc_dvfs_latency_response response;
+	struct tegra_bpmp_message msg;
+	struct tegra186_emc *emc;
+	unsigned int i;
+	int err;
+
+	emc = devm_kzalloc(&pdev->dev, sizeof(*emc), GFP_KERNEL);
+	if (!emc)
+		return -ENOMEM;
+
+	emc->bpmp = tegra_bpmp_get(&pdev->dev);
+	if (IS_ERR(emc->bpmp)) {
+		err = PTR_ERR(emc->bpmp);
+
+		if (err != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "failed to get BPMP: %d\n", err);
+
+		return err;
+	}
+
+	emc->clk = devm_clk_get(&pdev->dev, "emc");
+	if (IS_ERR(emc->clk)) {
+		err = PTR_ERR(emc->clk);
+		dev_err(&pdev->dev, "failed to get EMC clock: %d\n", err);
+		return err;
+	}
+
+	platform_set_drvdata(pdev, emc);
+	emc->dev = &pdev->dev;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.mrq = MRQ_EMC_DVFS_LATENCY;
+	msg.tx.data = NULL;
+	msg.tx.size = 0;
+	msg.rx.data = &response;
+	msg.rx.size = sizeof(response);
+
+	err = tegra_bpmp_transfer(emc->bpmp, &msg);
+	if (err < 0) {
+		dev_err(&pdev->dev, "failed to EMC DVFS pairs: %d\n", err);
+		return err;
+	}
+
+	emc->debugfs.min_rate = ULONG_MAX;
+	emc->debugfs.max_rate = 0;
+
+	emc->num_dvfs = response.num_pairs;
+
+	emc->dvfs = devm_kmalloc_array(&pdev->dev, emc->num_dvfs,
+				       sizeof(*emc->dvfs), GFP_KERNEL);
+	if (!emc->dvfs)
+		return -ENOMEM;
+
+	dev_dbg(&pdev->dev, "%u DVFS pairs:\n", emc->num_dvfs);
+
+	for (i = 0; i < emc->num_dvfs; i++) {
+		emc->dvfs[i].rate = response.pairs[i].freq * 1000;
+		emc->dvfs[i].latency = response.pairs[i].latency;
+
+		if (emc->dvfs[i].rate < emc->debugfs.min_rate)
+			emc->debugfs.min_rate = emc->dvfs[i].rate;
+
+		if (emc->dvfs[i].rate > emc->debugfs.max_rate)
+			emc->debugfs.max_rate = emc->dvfs[i].rate;
+
+		dev_dbg(&pdev->dev, "  %2u: %lu Hz -> %lu us\n", i,
+			emc->dvfs[i].rate, emc->dvfs[i].latency);
+	}
+
+	err = clk_set_rate_range(emc->clk, emc->debugfs.min_rate,
+				 emc->debugfs.max_rate);
+	if (err < 0) {
+		dev_err(&pdev->dev,
+			"failed to set rate range [%lu-%lu] for %pC\n",
+			emc->debugfs.min_rate, emc->debugfs.max_rate,
+			emc->clk);
+		return err;
+	}
+
+	emc->debugfs.root = debugfs_create_dir("emc", NULL);
+	if (!emc->debugfs.root) {
+		dev_err(&pdev->dev, "failed to create debugfs directory\n");
+		return 0;
+	}
+
+	debugfs_create_file("available_rates", S_IRUGO, emc->debugfs.root,
+			    emc, &tegra186_emc_debug_available_rates_fops);
+	debugfs_create_file("min_rate", S_IRUGO | S_IWUSR, emc->debugfs.root,
+			    emc, &tegra186_emc_debug_min_rate_fops);
+	debugfs_create_file("max_rate", S_IRUGO | S_IWUSR, emc->debugfs.root,
+			    emc, &tegra186_emc_debug_max_rate_fops);
+
+	return 0;
+}
+
+static int tegra186_emc_remove(struct platform_device *pdev)
+{
+	struct tegra186_emc *emc = platform_get_drvdata(pdev);
+
+	debugfs_remove_recursive(emc->debugfs.root);
+	tegra_bpmp_put(emc->bpmp);
+
+	return 0;
+}
+
+static const struct of_device_id tegra186_emc_of_match[] = {
+	{ .compatible = "nvidia,tegra186-emc" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, tegra186_emc_of_match);
+
+static struct platform_driver tegra186_emc_driver = {
+	.driver = {
+		.name = "tegra186-emc",
+		.of_match_table = tegra186_emc_of_match,
+		.suppress_bind_attrs = true,
+	},
+	.probe = tegra186_emc_probe,
+	.remove = tegra186_emc_remove,
+};
+module_platform_driver(tegra186_emc_driver);
+
+MODULE_AUTHOR("Thierry Reding <treding@nvidia.com>");
+MODULE_DESCRIPTION("NVIDIA Tegra186 External Memory Controller driver");
+MODULE_LICENSE("GPL v2");

drivers/memory/tegra/tegra186.c

@@ -590,10 +590,23 @@ static int tegra186_mc_probe(struct platform_device *pdev)
 
 	mc->dev = &pdev->dev;
 
+	err = of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);
+	if (err < 0)
+		return err;
+
 	platform_set_drvdata(pdev, mc);
 	tegra186_mc_program_sid(mc);
 
-	return err;
+	return 0;
+}
+
+static int tegra186_mc_remove(struct platform_device *pdev)
+{
+	struct tegra186_mc *mc = platform_get_drvdata(pdev);
+
+	of_platform_depopulate(mc->dev);
+
+	return 0;
 }
 
 static const struct of_device_id tegra186_mc_of_match[] = {
@@ -627,8 +640,8 @@ static struct platform_driver tegra186_mc_driver = {
 		.pm = &tegra186_mc_pm_ops,
 		.suppress_bind_attrs = true,
 	},
-	.prevent_deferred_probe = true,
 	.probe = tegra186_mc_probe,
+	.remove = tegra186_mc_remove,
 };
 module_platform_driver(tegra186_mc_driver);