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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Mon, 2 Sep 2019 23:08:08 +0200
Message-ID: <CAJZ5v0iF=TxxD_gCJfaZzORTrcu+2StJE1_vhthB70jxqCkHuw@mail.gmail.com>
Subject: Re: [PATCH 1/3] ACPI: Remove acpi_has_method() call from acpi_adxl.c
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Kelsey Skunberg <skunberg.kelsey@gmail.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>,
        ACPI Devel Mailing List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        skhan@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org, bjorn@helgaas.com,
        Tony Luck <tony.luck@intel.com>, Borislav Petkov <bp@alien8.de>
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Sorry for the delayed reply.

On Mon, Jul 22, 2019 at 8:29 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> [+cc Tony (original author), Borislav (merged original patch)]
>
> On Mon, Jul 22, 2019 at 10:31:11AM +0200, Rafael J. Wysocki wrote:
> > On Mon, Jul 22, 2019 at 4:36 AM Kelsey Skunberg
> > <skunberg.kelsey@gmail.com> wrote:
> > >
> > > acpi_check_dsm() will already return an error if the DSM method does not
> > > exist. Checking if the DSM method exists before the acpi_check_dsm() call
> > > is not needed. Remove acpi_has_method() call to avoid additional work.
> > >
> > > Signed-off-by: Kelsey Skunberg <skunberg.kelsey@gmail.com>
> > > ---
> > >  drivers/acpi/acpi_adxl.c | 5 -----
> > >  1 file changed, 5 deletions(-)
> > >
> > > diff --git a/drivers/acpi/acpi_adxl.c b/drivers/acpi/acpi_adxl.c
> > > index 13c8f7b50c46..89aac15663fd 100644
> > > --- a/drivers/acpi/acpi_adxl.c
> > > +++ b/drivers/acpi/acpi_adxl.c
> > > @@ -148,11 +148,6 @@ static int __init adxl_init(void)
> > >                 return -ENODEV;
> > >         }
> > >
> > > -       if (!acpi_has_method(handle, "_DSM")) {
> > > -               pr_info("No DSM method\n");
> >
> > And why is printing the message not useful?
> >
> > > -               return -ENODEV;
> > > -       }
> > > -
> > >         if (!acpi_check_dsm(handle, &adxl_guid, ADXL_REVISION,
> > >                             ADXL_IDX_GET_ADDR_PARAMS |
> > >                             ADXL_IDX_FORWARD_TRANSLATE)) {
>
> The next line of context (not included in the patch):
>
>                pr_info("DSM method does not support forward translate\n");
>
> IMHO kernel messages that are just a constant string, with no context
> or variable part (device ID, path, error code, etc) are questionable
> in general.  Is there any dev_printk()-like thing that takes an
> acpi_handle?  Seems like that would be useful for cases like this.
>
> This message *does* include an "ADXL: " prefix (from the pr_fmt
> definition), and from reading the code you can see that the only
> possible method is "\_SB.ADXL._DSM".
>
> There's nothing an end user can do with these messages, so I suspect
> their value is for debugging during platform bringup, and it would be
> sufficient to drop the first one (as Kelsey's patch does) and change
> the second one like this:
>
> -              pr_info("DSM method does not support forward translate\n");
> +              pr_info("%s DSM missing or does not support forward translate\n",
> +                      path);

You have a point, but then I would expect the changelog to mention that.

As it stands, the patch does more than the changelog says, which isn't nice.