memory: tegra: Expose supported rates via debugfs

In order to ease testing, expose the list of supported EMC frequencies
via debugfs.
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/memory/tegra/tegra124-emc.c

@@ -1027,7 +1027,40 @@ static int emc_debug_rate_set(void *data, u64 rate)
 DEFINE_SIMPLE_ATTRIBUTE(emc_debug_rate_fops, emc_debug_rate_get,
 			emc_debug_rate_set, "%lld\n");
 
-static void emc_debugfs_init(struct device *dev)
+static int emc_debug_supported_rates_show(struct seq_file *s, void *data)
+{
+	struct tegra_emc *emc = s->private;
+	const char *prefix = "";
+	unsigned int i;
+
+	for (i = 0; i < emc->num_timings; i++) {
+		struct emc_timing *timing = &emc->timings[i];
+
+		seq_printf(s, "%s%lu", prefix, timing->rate);
+
+		prefix = " ";
+	}
+
+	seq_puts(s, "\n");
+
+	return 0;
+}
+
+static int emc_debug_supported_rates_open(struct inode *inode,
+					  struct file *file)
+{
+	return single_open(file, emc_debug_supported_rates_show,
+			   inode->i_private);
+}
+
+static const struct file_operations emc_debug_supported_rates_fops = {
+	.open = emc_debug_supported_rates_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
+static void emc_debugfs_init(struct device *dev, struct tegra_emc *emc)
 {
 	struct dentry *root, *file;
 	struct clk *clk;
@@ -1048,6 +1081,11 @@ static void emc_debugfs_init(struct device *dev)
 				   &emc_debug_rate_fops);
 	if (!file)
 		dev_err(dev, "failed to create debugfs entry\n");
+
+	file = debugfs_create_file("supported_rates", S_IRUGO, root, emc,
+				   &emc_debug_supported_rates_fops);
+	if (!file)
+		dev_err(dev, "failed to create debugfs entry\n");
 }
 
 static int tegra_emc_probe(struct platform_device *pdev)
@@ -1119,7 +1157,7 @@ static int tegra_emc_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, emc);
 
 	if (IS_ENABLED(CONFIG_DEBUG_FS))
-		emc_debugfs_init(&pdev->dev);
+		emc_debugfs_init(&pdev->dev, emc);
 
 	return 0;
 };