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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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