usb: ulpi: Add debugfs support

This adds a debugfs file for ULPI devices which contains a dump of their
registers. This is useful for debugging basic connectivity problems. The
file is created in ulpi_register because many devices will never have a
driver bound (as they are managed in hardware by the USB controller
device).

The root directory of this subsystem is created before we register the
bus to ensure that devices can always create their directories.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20220127190004.1446909-4-sean.anderson@seco.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/common/ulpi.c

@@ -13,6 +13,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/acpi.h>
+#include <linux/debugfs.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/clk/clk-conf.h>
@@ -232,9 +233,64 @@ static int ulpi_read_id(struct ulpi *ulpi)
 	return 0;
 }
 
+static int ulpi_regs_read(struct seq_file *seq, void *data)
+{
+	struct ulpi *ulpi = seq->private;
+
+#define ulpi_print(name, reg) do { \
+	int ret = ulpi_read(ulpi, reg); \
+	if (ret < 0) \
+		return ret; \
+	seq_printf(seq, name " %.02x\n", ret); \
+} while (0)
+
+	ulpi_print("Vendor ID Low               ", ULPI_VENDOR_ID_LOW);
+	ulpi_print("Vendor ID High              ", ULPI_VENDOR_ID_HIGH);
+	ulpi_print("Product ID Low              ", ULPI_PRODUCT_ID_LOW);
+	ulpi_print("Product ID High             ", ULPI_PRODUCT_ID_HIGH);
+	ulpi_print("Function Control            ", ULPI_FUNC_CTRL);
+	ulpi_print("Interface Control           ", ULPI_IFC_CTRL);
+	ulpi_print("OTG Control                 ", ULPI_OTG_CTRL);
+	ulpi_print("USB Interrupt Enable Rising ", ULPI_USB_INT_EN_RISE);
+	ulpi_print("USB Interrupt Enable Falling", ULPI_USB_INT_EN_FALL);
+	ulpi_print("USB Interrupt Status        ", ULPI_USB_INT_STS);
+	ulpi_print("USB Interrupt Latch         ", ULPI_USB_INT_LATCH);
+	ulpi_print("Debug                       ", ULPI_DEBUG);
+	ulpi_print("Scratch Register            ", ULPI_SCRATCH);
+	ulpi_print("Carkit Control              ", ULPI_CARKIT_CTRL);
+	ulpi_print("Carkit Interrupt Delay      ", ULPI_CARKIT_INT_DELAY);
+	ulpi_print("Carkit Interrupt Enable     ", ULPI_CARKIT_INT_EN);
+	ulpi_print("Carkit Interrupt Status     ", ULPI_CARKIT_INT_STS);
+	ulpi_print("Carkit Interrupt Latch      ", ULPI_CARKIT_INT_LATCH);
+	ulpi_print("Carkit Pulse Control        ", ULPI_CARKIT_PLS_CTRL);
+	ulpi_print("Transmit Positive Width     ", ULPI_TX_POS_WIDTH);
+	ulpi_print("Transmit Negative Width     ", ULPI_TX_NEG_WIDTH);
+	ulpi_print("Receive Polarity Recovery   ", ULPI_POLARITY_RECOVERY);
+
+	return 0;
+}
+
+static int ulpi_regs_open(struct inode *inode, struct file *f)
+{
+	struct ulpi *ulpi = inode->i_private;
+
+	return single_open(f, ulpi_regs_read, ulpi);
+}
+
+static const struct file_operations ulpi_regs_ops = {
+	.owner = THIS_MODULE,
+	.open = ulpi_regs_open,
+	.release = single_release,
+	.read = seq_read,
+	.llseek = seq_lseek
+};
+
+#define ULPI_ROOT debugfs_lookup(KBUILD_MODNAME, NULL)
+
 static int ulpi_register(struct device *dev, struct ulpi *ulpi)
 {
 	int ret;
+	struct dentry *root;
 
 	ulpi->dev.parent = dev; /* needed early for ops */
 	ulpi->dev.bus = &ulpi_bus;
@@ -259,6 +315,9 @@ static int ulpi_register(struct device *dev, struct ulpi *ulpi)
 		return ret;
 	}
 
+	root = debugfs_create_dir(dev_name(dev), ULPI_ROOT);
+	debugfs_create_file("regs", 0444, root, ulpi, &ulpi_regs_ops);
+
 	dev_dbg(&ulpi->dev, "registered ULPI PHY: vendor %04x, product %04x\n",
 		ulpi->id.vendor, ulpi->id.product);
 
@@ -304,6 +363,8 @@ EXPORT_SYMBOL_GPL(ulpi_register_interface);
  */
 void ulpi_unregister_interface(struct ulpi *ulpi)
 {
+	debugfs_remove_recursive(debugfs_lookup(dev_name(&ulpi->dev),
+						ULPI_ROOT));
 	device_unregister(&ulpi->dev);
 }
 EXPORT_SYMBOL_GPL(ulpi_unregister_interface);
@@ -312,13 +373,21 @@ EXPORT_SYMBOL_GPL(ulpi_unregister_interface);
 
 static int __init ulpi_init(void)
 {
-	return bus_register(&ulpi_bus);
+	int ret;
+	struct dentry *root;
+
+	root = debugfs_create_dir(KBUILD_MODNAME, NULL);
+	ret = bus_register(&ulpi_bus);
+	if (ret)
+		debugfs_remove(root);
+	return ret;
 }
 subsys_initcall(ulpi_init);
 
 static void __exit ulpi_exit(void)
 {
 	bus_unregister(&ulpi_bus);
+	debugfs_remove_recursive(ULPI_ROOT);
 }
 module_exit(ulpi_exit);