linux-kernel - Re: [PATCH 1/2] debugfs: regset32: Add Runtime PM support

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Date:   Fri, 31 Jan 2020 11:13:33 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Felipe Balbi <balbi@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Bin Liu <b-liu@...com>, linux-crypto@...r.kernel.org,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] debugfs: regset32: Add Runtime PM support

On Fri, Jan 24, 2020 at 2:30 PM Geert Uytterhoeven
<geert+renesas@...der.be> 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 <geert+renesas@...der.be>

LGTM:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  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
>