linux-kernel - [PATCH 19/23] gpio: mockup: add a symlink for the per-chip debugfs directory

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Date:   Fri,  4 Sep 2020 17:45:43 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>
Cc:     linux-gpio@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: [PATCH 19/23] gpio: mockup: add a symlink for the per-chip debugfs directory

From: Bartosz Golaszewski <bgolaszewski@...libre.com>

We used to have a symlink named after the chip's label linking to the
per-chip directory named after the chip's name. This was removed by
commit d51ee07a8de7 ("gpio: mockup: don't create the debugfs link named
after the label") because there were no users of it.

This changeset proposes to reintroduce debugfs symlinks but inverted:
the link named after the device name points to the directory named after
the label. This way user-space can dynamically create a chip (once that
functionality is available), detect its creation over uevent and match
the device name to the label by resolving the link.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
---
 drivers/gpio/gpio-mockup.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-mockup.c b/drivers/gpio/gpio-mockup.c
index 7df990662c17..bc4609e047ef 100644
--- a/drivers/gpio/gpio-mockup.c
+++ b/drivers/gpio/gpio-mockup.c
@@ -52,6 +52,7 @@ struct gpio_mockup_chip {
 	struct gpio_mockup_line_status *lines;
 	struct irq_domain *irq_sim_domain;
 	struct dentry *dbg_dir;
+	struct dentry *dbg_link;
 	struct mutex lock;
 };
 
@@ -355,6 +356,13 @@ static void gpio_mockup_remove_chip_debugfs_entry(void *data)
 	debugfs_remove_recursive(entry);
 }
 
+static void gpio_mockup_remove_chip_debugfs_link(void *data)
+{
+	struct dentry *link = data;
+
+	debugfs_remove(link);
+}
+
 static int gpio_mockup_debugfs_setup(struct device *dev,
 				     struct gpio_mockup_chip *chip)
 {
@@ -368,7 +376,7 @@ static int gpio_mockup_debugfs_setup(struct device *dev,
 	gc = &chip->gc;
 	devname = dev_name(&gc->gpiodev->dev);
 
-	chip->dbg_dir = debugfs_create_dir(devname, gpio_mockup_dbg_dir);
+	chip->dbg_dir = debugfs_create_dir(gc->label, gpio_mockup_dbg_dir);
 	if (IS_ERR(chip->dbg_dir))
 		return PTR_ERR(chip->dbg_dir);
 
@@ -377,6 +385,16 @@ static int gpio_mockup_debugfs_setup(struct device *dev,
 	if (ret)
 		return ret;
 
+	chip->dbg_link = debugfs_create_symlink(devname, gpio_mockup_dbg_dir,
+						gc->label);
+	if (IS_ERR(chip->dbg_link))
+		return PTR_ERR(chip->dbg_link);
+
+	ret = devm_add_action_or_reset(dev,
+			gpio_mockup_remove_chip_debugfs_link, chip->dbg_link);
+	if (ret)
+		return ret;
+
 	for (i = 0; i < gc->ngpio; i++) {
 		name = devm_kasprintf(dev, GFP_KERNEL, "%d", i);
 		if (!name)
-- 
2.26.1