linux-kernel - Re: [PATCH 1/3] ACPI: Remove acpi_has_method() call from acpi

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Date:   Mon, 22 Jul 2019 13:29:29 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Kelsey Skunberg <skunberg.kelsey@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        ACPI Devel Mailing List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        skhan@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org, bjorn@...gaas.com,
        Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 1/3] ACPI: Remove acpi_has_method() call from acpi_adxl.c

[+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@...il.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@...il.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);