[PATCH 1/2] debugfs: regset32: Add Runtime PM support

[Geert Uytterhoeven]

Hardware registers of devices under control of power management cannot
be accessed at all times.  If such a device is suspended, register
accesses may lead to undefined behavior, like reading bogus values, or
causing exceptions or system locks.

Extend struct debugfs_regset32 with an optional field to let device
drivers specify the device the registers in the set belong to.  This
allows debugfs_show_regset32() to make sure the device is resumed while
its registers are being read.

Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
---
 fs/debugfs/file.c       | 8 ++++++++
 include/linux/debugfs.h | 1 +
 2 files changed, 9 insertions(+)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index dede25247b81f72a..5e52d68421c678f2 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/atomic.h>
 #include <linux/device.h>
+#include <linux/pm_runtime.h>
 #include <linux/poll.h>
 #include <linux/security.h>
 
@@ -1057,7 +1058,14 @@ static int debugfs_show_regset32(struct seq_file *s, void *data)
 {
 	struct debugfs_regset32 *regset = s->private;
 
+	if (regset->dev)
+		pm_runtime_get_sync(regset->dev);
+
 	debugfs_print_regs32(s, regset->regs, regset->nregs, regset->base, "");
+
+	if (regset->dev)
+		pm_runtime_put(regset->dev);
+
 	return 0;
 }
 
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index bf9b6cafa4c26a68..5d0783ae09f365ac 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -35,6 +35,7 @@ struct debugfs_regset32 {
 	const struct debugfs_reg32 *regs;
 	int nregs;
 	void __iomem *base;
+	struct device *dev;	/* Optional device for Runtime PM */
 };
 
 extern struct dentry *arch_debugfs_dir;
-- 
2.17.1