firmware/raspberrypi: Add a get_throttled sysfs file

drivers/firmware/raspberrypi.c

@@ -14,18 +14,22 @@
 #include <linux/module.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/workqueue.h>
 #include <soc/bcm2835/raspberrypi-firmware.h>
 
 #define MBOX_MSG(chan, data28)		(((data28) & ~0xf) | ((chan) & 0xf))
 #define MBOX_CHAN(msg)			((msg) & 0xf)
 #define MBOX_DATA28(msg)		((msg) & ~0xf)
 #define MBOX_CHAN_PROPERTY		8
 
+#define UNDERVOLTAGE_BIT		BIT(0)
+
 struct rpi_firmware {
 	struct mbox_client cl;
 	struct mbox_chan *chan; /* The property channel. */
 	struct completion c;
 	u32 enabled;
+	struct delayed_work get_throttled_poll_work;
 };
 
 static struct platform_device *g_pdev;
@@ -166,6 +170,101 @@ int rpi_firmware_property(struct rpi_firmware *fw,
 }
 EXPORT_SYMBOL_GPL(rpi_firmware_property);
 
+static int rpi_firmware_get_throttled(struct rpi_firmware *fw, u32 *value)
+{
+	static ktime_t old_timestamp;
+	static u32 old_value;
+	u32 new_sticky, old_sticky, new_uv, old_uv;
+	ktime_t new_timestamp;
+	s64 elapsed_ms;
+	int ret;
+
+	if (!fw)
+		return -EBUSY;
+
+	/*
+	 * We can't run faster than the sticky shift (100ms) since we get
+	 * flipping in the sticky bits that are cleared.
+	 * This happens on polling, so just return the previous value.
+	 */
+	new_timestamp = ktime_get();
+	elapsed_ms = ktime_ms_delta(new_timestamp, old_timestamp);
+	if (elapsed_ms < 150) {
+		*value = old_value;
+		return 0;
+	}
+	old_timestamp = new_timestamp;
+
+	/* Clear sticky bits */
+	*value = 0xffff;
+
+	ret = rpi_firmware_property(fw, RPI_FIRMWARE_GET_THROTTLED,
+				    value, sizeof(*value));
+	if (ret)
+		return ret;
+
+	new_sticky = *value >> 16;
+	old_sticky = old_value >> 16;
+	old_value = *value;
+
+	/* Only notify about changes in the sticky bits */
+	if (new_sticky == old_sticky)
+		return 0;
+
+	new_uv = new_sticky & UNDERVOLTAGE_BIT;
+	old_uv = old_sticky & UNDERVOLTAGE_BIT;
+
+	if (new_uv != old_uv) {
+		if (new_uv)
+			pr_crit("Under-voltage detected! (0x%08x)\n", *value);
+		else
+			pr_info("Voltage normalised (0x%08x)\n", *value);
+	}
+
+	sysfs_notify(&fw->cl.dev->kobj, NULL, "get_throttled");
+
+	return 0;
+}
+
+static void get_throttled_poll(struct work_struct *work)
+{
+	struct rpi_firmware *fw = container_of(work, struct rpi_firmware,
+					       get_throttled_poll_work.work);
+	u32 dummy;
+	int ret;
+
+	ret = rpi_firmware_get_throttled(fw, &dummy);
+	if (ret)
+		pr_debug("%s: Failed to read value (%d)", __func__, ret);
+
+	schedule_delayed_work(&fw->get_throttled_poll_work, 2 * HZ);
+}
+
+static ssize_t get_throttled_show(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	struct rpi_firmware *fw = dev_get_drvdata(dev);
+	u32 value;
+	int ret;
+
+	ret = rpi_firmware_get_throttled(fw, &value);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%x\n", value);
+}
+
+static DEVICE_ATTR_RO(get_throttled);
+
+static struct attribute *rpi_firmware_dev_attrs[] = {
+	&dev_attr_get_throttled.attr,
+	NULL,
+};
+
+static const struct attribute_group rpi_firmware_dev_group = {
+	.attrs = rpi_firmware_dev_attrs,
+};
+
 static void
 rpi_firmware_print_firmware_revision(struct rpi_firmware *fw)
 {
@@ -190,6 +289,11 @@ static int rpi_firmware_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct rpi_firmware *fw;
+	int ret;
+
+	ret = devm_device_add_group(dev, &rpi_firmware_dev_group);
+	if (ret)
+		return ret;
 
 	fw = devm_kzalloc(dev, sizeof(*fw), GFP_KERNEL);
 	if (!fw)
@@ -208,19 +312,23 @@ static int rpi_firmware_probe(struct platform_device *pdev)
 	}
 
 	init_completion(&fw->c);
+	INIT_DELAYED_WORK(&fw->get_throttled_poll_work, get_throttled_poll);
 
 	platform_set_drvdata(pdev, fw);
 	g_pdev = pdev;
 
 	rpi_firmware_print_firmware_revision(fw);
 
+	schedule_delayed_work(&fw->get_throttled_poll_work, 0);
+
 	return 0;
 }
 
 static int rpi_firmware_remove(struct platform_device *pdev)
 {
 	struct rpi_firmware *fw = platform_get_drvdata(pdev);
 
+	cancel_delayed_work_sync(&fw->get_throttled_poll_work);
 	mbox_free_channel(fw->chan);
 	g_pdev = NULL;
 

include/soc/bcm2835/raspberrypi-firmware.h

@@ -77,6 +77,7 @@ enum rpi_firmware_property_tag {
 	RPI_FIRMWARE_GET_EDID_BLOCK =                         0x00030020,
 	RPI_FIRMWARE_GET_CUSTOMER_OTP =                       0x00030021,
 	RPI_FIRMWARE_GET_DOMAIN_STATE =                       0x00030030,
+	RPI_FIRMWARE_GET_THROTTLED =                          0x00030046,
 	RPI_FIRMWARE_SET_CLOCK_STATE =                        0x00038001,
 	RPI_FIRMWARE_SET_CLOCK_RATE =                         0x00038002,
 	RPI_FIRMWARE_SET_VOLTAGE =                            0x00038003,