cpufreq: brcmstb-avs-cpufreq: add debugfs support

In order to aid debugging, we add a debugfs interface to the driver
that allows direct interaction with the AVS co-processor.

The debugfs interface provides a means for reading all and writing some
of the mailbox registers directly from the shell prompt and enables a
user to execute the communications protocol between ARM CPU and AVS CPU
step-by-step.

This interface should be used for debugging purposes only.
Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/Kconfig.arm

@@ -23,6 +23,16 @@ config ARM_BRCMSTB_AVS_CPUFREQ
 
 	  Say Y, if you have a Broadcom SoC with AVS support for DFS or DVFS.
 
+config ARM_BRCMSTB_AVS_CPUFREQ_DEBUG
+	bool "Broadcom STB AVS CPUfreq driver sysfs debug capability"
+	depends on ARM_BRCMSTB_AVS_CPUFREQ
+	help
+	  Enabling this option turns on debug support via sysfs under
+	  /sys/kernel/debug/brcmstb-avs-cpufreq. It is possible to read all and
+	  write some AVS mailbox registers through sysfs entries.
+
+	  If in doubt, say N.
+
 config ARM_DT_BL_CPUFREQ
 	tristate "Generic probing via DT for ARM big LITTLE CPUfreq driver"
 	depends on ARM_BIG_LITTLE_CPUFREQ && OF

drivers/cpufreq/brcmstb-avs-cpufreq.c

@@ -49,6 +49,13 @@
 #include <linux/platform_device.h>
 #include <linux/semaphore.h>
 
+#ifdef CONFIG_ARM_BRCMSTB_AVS_CPUFREQ_DEBUG
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#endif
+
 /* Max number of arguments AVS calls take */
 #define AVS_MAX_CMD_ARGS	4
 /*
@@ -175,11 +182,88 @@ struct private_data {
 	void __iomem *base;
 	void __iomem *avs_intr_base;
 	struct device *dev;
+#ifdef CONFIG_ARM_BRCMSTB_AVS_CPUFREQ_DEBUG
+	struct dentry *debugfs;
+#endif
 	struct completion done;
 	struct semaphore sem;
 	struct pmap pmap;
 };
 
+#ifdef CONFIG_ARM_BRCMSTB_AVS_CPUFREQ_DEBUG
+
+enum debugfs_format {
+	DEBUGFS_NORMAL,
+	DEBUGFS_FLOAT,
+	DEBUGFS_REV,
+};
+
+struct debugfs_data {
+	struct debugfs_entry *entry;
+	struct private_data *priv;
+};
+
+struct debugfs_entry {
+	char *name;
+	u32 offset;
+	fmode_t mode;
+	enum debugfs_format format;
+};
+
+#define DEBUGFS_ENTRY(name, mode, format)	{ \
+	#name, AVS_MBOX_##name, mode, format \
+}
+
+/*
+ * These are used for debugfs only. Otherwise we use AVS_MBOX_PARAM() directly.
+ */
+#define AVS_MBOX_PARAM1		AVS_MBOX_PARAM(0)
+#define AVS_MBOX_PARAM2		AVS_MBOX_PARAM(1)
+#define AVS_MBOX_PARAM3		AVS_MBOX_PARAM(2)
+#define AVS_MBOX_PARAM4		AVS_MBOX_PARAM(3)
+
+/*
+ * This table stores the name, access permissions and offset for each hardware
+ * register and is used to generate debugfs entries.
+ */
+static struct debugfs_entry debugfs_entries[] = {
+	DEBUGFS_ENTRY(COMMAND, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(STATUS, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(VOLTAGE0, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(TEMP0, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(PV0, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(MV0, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(PARAM1, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(PARAM2, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(PARAM3, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(PARAM4, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(REVISION, 0, DEBUGFS_REV),
+	DEBUGFS_ENTRY(PSTATE, 0, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(HEARTBEAT, 0, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(MAGIC, S_IWUSR, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(SIGMA_HVT, 0, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(SIGMA_SVT, 0, DEBUGFS_NORMAL),
+	DEBUGFS_ENTRY(VOLTAGE1, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(TEMP1, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(PV1, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(MV1, 0, DEBUGFS_FLOAT),
+	DEBUGFS_ENTRY(FREQUENCY, 0, DEBUGFS_NORMAL),
+};
+
+static int brcm_avs_target_index(struct cpufreq_policy *, unsigned int);
+
+static char *__strtolower(char *s)
+{
+	char *p;
+
+	for (p = s; *p; p++)
+		*p = tolower(*p);
+
+	return s;
+}
+
+#endif /* CONFIG_ARM_BRCMSTB_AVS_CPUFREQ_DEBUG */
+
 static void __iomem *__map_region(const char *name)
 {
 	struct device_node *np;
@@ -432,6 +516,238 @@ brcm_avs_get_freq_table(struct device *dev, struct private_data *priv)
 	return table;
 }
 
+#ifdef CONFIG_ARM_BRCMSTB_AVS_CPUFREQ_DEBUG
+
+#define MANT(x)	(unsigned int)(abs((x)) / 1000)
+#define FRAC(x)	(unsigned int)(abs((x)) - abs((x)) / 1000 * 1000)
+
+static int brcm_avs_debug_show(struct seq_file *s, void *data)
+{
+	struct debugfs_data *dbgfs = s->private;
+	void __iomem *base;
+	u32 val, offset;
+
+	if (!dbgfs) {
+		seq_puts(s, "No device pointer\n");
+		return 0;
+	}
+
+	base = dbgfs->priv->base;
+	offset = dbgfs->entry->offset;
+	val = readl(base + offset);
+	switch (dbgfs->entry->format) {
+	case DEBUGFS_NORMAL:
+		seq_printf(s, "%u\n", val);
+		break;
+	case DEBUGFS_FLOAT:
+		seq_printf(s, "%d.%03d\n", MANT(val), FRAC(val));
+		break;
+	case DEBUGFS_REV:
+		seq_printf(s, "%c.%c.%c.%c\n", (val >> 24 & 0xff),
+			   (val >> 16 & 0xff), (val >> 8 & 0xff),
+			   val & 0xff);
+		break;
+	}
+	seq_printf(s, "0x%08x\n", val);
+
+	return 0;
+}
+
+#undef MANT
+#undef FRAC
+
+static ssize_t brcm_avs_seq_write(struct file *file, const char __user *buf,
+				  size_t size, loff_t *ppos)
+{
+	struct seq_file *s = file->private_data;
+	struct debugfs_data *dbgfs = s->private;
+	struct private_data *priv = dbgfs->priv;
+	void __iomem *base, *avs_intr_base;
+	bool use_issue_command = false;
+	unsigned long val, offset;
+	char str[128];
+	int ret;
+	char *str_ptr = str;
+
+	if (size >= sizeof(str))
+		return -E2BIG;
+
+	memset(str, 0, sizeof(str));
+	ret = copy_from_user(str, buf, size);
+	if (ret)
+		return ret;
+
+	base = priv->base;
+	avs_intr_base = priv->avs_intr_base;
+	offset = dbgfs->entry->offset;
+	/*
+	 * Special case writing to "command" entry only: if the string starts
+	 * with a 'c', we use the driver's __issue_avs_command() function.
+	 * Otherwise, we perform a raw write. This should allow testing of raw
+	 * access as well as using the higher level function. (Raw access
+	 * doesn't clear the firmware return status after issuing the command.)
+	 */
+	if (str_ptr[0] == 'c' && offset == AVS_MBOX_COMMAND) {
+		use_issue_command = true;
+		str_ptr++;
+	}
+	if (kstrtoul(str_ptr, 0, &val) != 0)
+		return -EINVAL;
+
+	/*
+	 * Setting the P-state is a special case. We need to update the CPU
+	 * frequency we report.
+	 */
+	if (val == AVS_CMD_SET_PSTATE) {
+		struct cpufreq_policy *policy;
+		unsigned int pstate;
+
+		policy = cpufreq_cpu_get(smp_processor_id());
+		/* Read back the P-state we are about to set */
+		pstate = readl(base + AVS_MBOX_PARAM(0));
+		if (use_issue_command) {
+			ret = brcm_avs_target_index(policy, pstate);
+			return ret ? ret : size;
+		}
+		policy->cur = policy->freq_table[pstate].frequency;
+	}
+
+	if (use_issue_command) {
+		ret = __issue_avs_command(priv, val, false, NULL);
+	} else {
+		/* Locking here is not perfect, but is only for debug. */
+		ret = down_interruptible(&priv->sem);
+		if (ret)
+			return ret;
+
+		writel(val, base + offset);
+		/* We have to wake up the firmware to process a command. */
+		if (offset == AVS_MBOX_COMMAND)
+			writel(AVS_CPU_L2_INT_MASK,
+			       avs_intr_base + AVS_CPU_L2_SET0);
+		up(&priv->sem);
+	}
+
+	return ret ? ret : size;
+}
+
+static struct debugfs_entry *__find_debugfs_entry(const char *name)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(debugfs_entries); i++)
+		if (strcasecmp(debugfs_entries[i].name, name) == 0)
+			return &debugfs_entries[i];
+
+	return NULL;
+}
+
+static int brcm_avs_debug_open(struct inode *inode, struct file *file)
+{
+	struct debugfs_data *data;
+	fmode_t fmode;
+	int ret;
+
+	/*
+	 * seq_open(), which is called by single_open(), clears "write" access.
+	 * We need write access to some files, so we preserve our access mode
+	 * and restore it.
+	 */
+	fmode = file->f_mode;
+	/*
+	 * Check access permissions even for root. We don't want to be writing
+	 * to read-only registers. Access for regular users has already been
+	 * checked by the VFS layer.
+	 */
+	if ((fmode & FMODE_WRITER) && !(inode->i_mode & S_IWUSR))
+		return -EACCES;
+
+	data = kmalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	/*
+	 * We use the same file system operations for all our debug files. To
+	 * produce specific output, we look up the file name upon opening a
+	 * debugfs entry and map it to a memory offset. This offset is then used
+	 * in the generic "show" function to read a specific register.
+	 */
+	data->entry = __find_debugfs_entry(file->f_path.dentry->d_iname);
+	data->priv = inode->i_private;
+
+	ret = single_open(file, brcm_avs_debug_show, data);
+	if (ret)
+		kfree(data);
+	file->f_mode = fmode;
+
+	return ret;
+}
+
+static int brcm_avs_debug_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq_priv = file->private_data;
+	struct debugfs_data *data = seq_priv->private;
+
+	kfree(data);
+	return single_release(inode, file);
+}
+
+static const struct file_operations brcm_avs_debug_ops = {
+	.open		= brcm_avs_debug_open,
+	.read		= seq_read,
+	.write		= brcm_avs_seq_write,
+	.llseek		= seq_lseek,
+	.release	= brcm_avs_debug_release,
+};
+
+static void brcm_avs_cpufreq_debug_init(struct platform_device *pdev)
+{
+	struct private_data *priv = platform_get_drvdata(pdev);
+	struct dentry *dir;
+	int i;
+
+	if (!priv)
+		return;
+
+	dir = debugfs_create_dir(BRCM_AVS_CPUFREQ_NAME, NULL);
+	if (IS_ERR_OR_NULL(dir))
+		return;
+	priv->debugfs = dir;
+
+	for (i = 0; i < ARRAY_SIZE(debugfs_entries); i++) {
+		/*
+		 * The DEBUGFS_ENTRY macro generates uppercase strings. We
+		 * convert them to lowercase before creating the debugfs
+		 * entries.
+		 */
+		char *entry = __strtolower(debugfs_entries[i].name);
+		fmode_t mode = debugfs_entries[i].mode;
+
+		if (!debugfs_create_file(entry, S_IFREG | S_IRUGO | mode,
+					 dir, priv, &brcm_avs_debug_ops)) {
+			priv->debugfs = NULL;
+			debugfs_remove_recursive(dir);
+			break;
+		}
+	}
+}
+
+static void brcm_avs_cpufreq_debug_exit(struct platform_device *pdev)
+{
+	struct private_data *priv = platform_get_drvdata(pdev);
+
+	if (priv && priv->debugfs) {
+		debugfs_remove_recursive(priv->debugfs);
+		priv->debugfs = NULL;
+	}
+}
+
+#else
+
+static void brcm_avs_cpufreq_debug_init(struct platform_device *pdev) {}
+static void brcm_avs_cpufreq_debug_exit(struct platform_device *pdev) {}
+
+#endif /* CONFIG_ARM_BRCMSTB_AVS_CPUFREQ_DEBUG */
+
 /*
  * To ensure the right firmware is running we need to
  *    - check the MAGIC matches what we expect
@@ -694,8 +1010,11 @@ static int brcm_avs_cpufreq_probe(struct platform_device *pdev)
 		return ret;
 
 	brcm_avs_driver.driver_data = pdev;
+	ret = cpufreq_register_driver(&brcm_avs_driver);
+	if (!ret)
+		brcm_avs_cpufreq_debug_init(pdev);
 
-	return cpufreq_register_driver(&brcm_avs_driver);
+	return ret;
 }
 
 static int brcm_avs_cpufreq_remove(struct platform_device *pdev)
@@ -707,6 +1026,8 @@ static int brcm_avs_cpufreq_remove(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	brcm_avs_cpufreq_debug_exit(pdev);
+
 	priv = platform_get_drvdata(pdev);
 	iounmap(priv->base);
 	iounmap(priv->avs_intr_base);