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Message-ID: <CAJZ5v0gmHPBS3LE+Eo8yJkvpuavBvip-1AEEEf9nxAp2gi_adQ@mail.gmail.com>
Date: Mon, 17 Jun 2024 20:43:03 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Len Brown <lenb@...nel.org>, Robert Moore <robert.moore@...el.com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, acpica-devel@...ts.linux.dev
Subject: Re: [PATCH 1/5] ACPI: sysfs: convert utf-16 from _STR to utf-8 only once

On Mon, Jun 17, 2024 at 8:37 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Jun 13, 2024 at 10:15 PM Thomas Weißschuh <linux@...ssschuh.net> wrote:
> >
> > The ACPI _STR method returns an UTF-16 string that is converted to utf-8
> > before printing it in sysfs.
> > Currently this conversion is performed every time the "description"
> > sysfs attribute is read, which is not necessary.
>
> Why is it a problem, though?
>
> How many devices have _STR and how much of the time is it used?
>
> Hint: On the system I'm sitting in front of, the answer is 0 and never.

This was actually factually incorrect, sorry.

The correct answer is 12 out of 247 and very rarely (if at all).
Which doesn't really change the point IMO.

> So Is it really worth adding an _STR string pointer to every struct acpi_device?
>
> > Only perform the conversion once and cache the result.
> >
> > Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> > ---
> >  drivers/acpi/device_sysfs.c | 63 ++++++++++++++++++++++++++++-----------------
> >  include/acpi/acpi_bus.h     |  2 +-
> >  2 files changed, 40 insertions(+), 25 deletions(-)
>
> And it's more lines of code even.
>
> >
> > diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
> > index 23373faa35ec..4bedbe8f57ed 100644
> > --- a/drivers/acpi/device_sysfs.c
> > +++ b/drivers/acpi/device_sysfs.c
> > @@ -439,24 +439,11 @@ static ssize_t description_show(struct device *dev,
> >                                 char *buf)
> >  {
> >         struct acpi_device *acpi_dev = to_acpi_device(dev);
> > -       int result;
> >
> > -       if (acpi_dev->pnp.str_obj == NULL)
> > +       if (acpi_dev->pnp.str == NULL)
> >                 return 0;
> >
> > -       /*
> > -        * The _STR object contains a Unicode identifier for a device.
> > -        * We need to convert to utf-8 so it can be displayed.
> > -        */
> > -       result = utf16s_to_utf8s(
> > -               (wchar_t *)acpi_dev->pnp.str_obj->buffer.pointer,
> > -               acpi_dev->pnp.str_obj->buffer.length,
> > -               UTF16_LITTLE_ENDIAN, buf,
> > -               PAGE_SIZE - 1);
> > -
> > -       buf[result++] = '\n';
> > -
> > -       return result;
> > +       return sysfs_emit("%s\n", acpi_dev->pnp.str);
> >  }
> >  static DEVICE_ATTR_RO(description);
> >
> > @@ -507,14 +494,46 @@ static ssize_t status_show(struct device *dev, struct device_attribute *attr,
> >  }
> >  static DEVICE_ATTR_RO(status);
> >
> > +static const char *acpi_device_str(struct acpi_device *dev)
> > +{
> > +       struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
> > +       union acpi_object *str_obj;
> > +       acpi_status status;
> > +       const char *ret;
> > +       char buf[512];
> > +       int result;
> > +
> > +       if (!acpi_has_method(dev->handle, "_STR"))
> > +               return NULL;
> > +
> > +       status = acpi_evaluate_object(dev->handle, "_STR",
> > +                                     NULL, &buffer);
> > +       if (ACPI_FAILURE(status))
> > +               return NULL;
> > +
> > +       str_obj = buffer.pointer;
> > +       /*
> > +        * The _STR object contains a Unicode identifier for a device.
> > +        * We need to convert to utf-8 so it can be displayed.
> > +        */
> > +       result = utf16s_to_utf8s((wchar_t *)str_obj->buffer.pointer,
> > +                                str_obj->buffer.length,
> > +                                UTF16_LITTLE_ENDIAN,
> > +                                buf, sizeof(buf) - 1);
> > +       buf[result++] = '\0';
> > +
> > +       ret = kstrdup(buf, GFP_KERNEL);
> > +       kfree(buffer.pointer);
> > +
> > +       return ret;
> > +}
> > +
> >  /**
> >   * acpi_device_setup_files - Create sysfs attributes of an ACPI device.
> >   * @dev: ACPI device object.
> >   */
> >  int acpi_device_setup_files(struct acpi_device *dev)
> >  {
> > -       struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
> > -       acpi_status status;
> >         int result = 0;
> >
> >         /*
> > @@ -539,12 +558,8 @@ int acpi_device_setup_files(struct acpi_device *dev)
> >         /*
> >          * If device has _STR, 'description' file is created
> >          */
> > -       if (acpi_has_method(dev->handle, "_STR")) {
> > -               status = acpi_evaluate_object(dev->handle, "_STR",
> > -                                       NULL, &buffer);
> > -               if (ACPI_FAILURE(status))
> > -                       buffer.pointer = NULL;
> > -               dev->pnp.str_obj = buffer.pointer;
> > +       dev->pnp.str = acpi_device_str(dev);
> > +       if (dev->pnp.str) {
> >                 result = device_create_file(&dev->dev, &dev_attr_description);
> >                 if (result)
> >                         goto end;
> > @@ -618,7 +633,7 @@ void acpi_device_remove_files(struct acpi_device *dev)
> >          * If device has _STR, remove 'description' file
> >          */
> >         if (acpi_has_method(dev->handle, "_STR")) {
> > -               kfree(dev->pnp.str_obj);
> > +               kfree(dev->pnp.str);
> >                 device_remove_file(&dev->dev, &dev_attr_description);
> >         }
> >         /*
> > diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> > index 1a4dfd7a1c4a..32e3105c9ece 100644
> > --- a/include/acpi/acpi_bus.h
> > +++ b/include/acpi/acpi_bus.h
> > @@ -254,7 +254,7 @@ struct acpi_device_pnp {
> >         struct list_head ids;           /* _HID and _CIDs */
> >         acpi_device_name device_name;   /* Driver-determined */
> >         acpi_device_class device_class; /*        "          */
> > -       union acpi_object *str_obj;     /* unicode string for _STR method */
> > +       const char *str;                /* _STR */
> >  };
> >
> >  #define acpi_device_bid(d)     ((d)->pnp.bus_id)
> >
> > --
> > 2.45.2
> >
> >

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