2020-01-24 14:36:56

by Geert Uytterhoeven

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

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 <[email protected]>
---
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

2020-01-31 10:14:07

by Rafael J. Wysocki

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

On Fri, Jan 24, 2020 at 2:30 PM Geert Uytterhoeven
<[email protected]> wrote:
>
> 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 <[email protected]>

LGTM:

Acked-by: Rafael J. Wysocki <[email protected]>

> ---
> 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
>