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Message-ID: <CAJZ5v0iHB1X7WM6Lg_-vr3Kzwp65yqjvHG9CA_X8vqFBFV_F_A@mail.gmail.com>
Date: Mon, 17 Jun 2024 20:37:40 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 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 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.
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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