linux-kernel - Re: [PATCH v5 11/20] ACPI: platform_profile: Add choices attribute for class interface

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Message-ID: <0ffe9b8b-814e-4b5a-a960-22797e327b4a@gmx.de>
Date: Fri, 8 Nov 2024 19:06:50 +0100
From: Armin Wolf <W_Armin@....de>
To: Mario Limonciello <mario.limonciello@....com>,
 Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Maximilian Luz <luzmaximilian@...il.com>, Lee Chun-Yi <jlee@...e.com>,
 Shyam Sundar S K <Shyam-sundar.S-k@....com>,
 Corentin Chary <corentin.chary@...il.com>, "Luke D . Jones"
 <luke@...nes.dev>, Ike Panhc <ike.pan@...onical.com>,
 Henrique de Moraes Holschuh <hmh@....eng.br>,
 Alexis Belmonte <alexbelm48@...il.com>,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
 Ai Chao <aichao@...inos.cn>, Gergo Koteles <soyer@....hu>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:ACPI" <linux-acpi@...r.kernel.org>,
 "open list:MICROSOFT SURFACE PLATFORM PROFILE DRIVER"
 <platform-driver-x86@...r.kernel.org>,
 "open list:THINKPAD ACPI EXTRAS DRIVER"
 <ibm-acpi-devel@...ts.sourceforge.net>,
 Mark Pearson <mpearson-lenovo@...ebb.ca>,
 Matthew Schwartz <matthew.schwartz@...ux.dev>
Subject: Re: [PATCH v5 11/20] ACPI: platform_profile: Add choices attribute
 for class interface

Am 07.11.24 um 23:09 schrieb Mario Limonciello:

> On 11/7/2024 02:28, Armin Wolf wrote:
>> Am 07.11.24 um 07:02 schrieb Mario Limonciello:
>>
>>> The `choices` file will show all possible choices that a given platform
>>> profile handler can support.
>>>
>>> Tested-by: Mark Pearson <mpearson-lenovo@...ebb.ca>
>>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>>> ---
>>> v5:
>>>   * Fix kdoc
>>>   * Add tag
>>>   * Fix whitespace
>>>   * Adjust mutex use
>>> ---
>>>   drivers/acpi/platform_profile.c | 65
>>> +++++++++++++++++++++++++++++++++
>>>   1 file changed, 65 insertions(+)
>>>
>>> diff --git a/drivers/acpi/platform_profile.c b/drivers/acpi/
>>> platform_profile.c
>>> index f605c2bd35c68..5e0bb91c5f451 100644
>>> --- a/drivers/acpi/platform_profile.c
>>> +++ b/drivers/acpi/platform_profile.c
>>> @@ -25,6 +25,46 @@ static_assert(ARRAY_SIZE(profile_names) ==
>>> PLATFORM_PROFILE_LAST);
>>>
>>>   static DEFINE_IDA(platform_profile_ida);
>>>
>>> +/**
>>> + * _commmon_choices_show - Show the available profile choices
>>> + * @choices: The available profile choices
>>> + * @buf: The buffer to write to
>>> + * Return: The number of bytes written
>>> + */
>>> +static ssize_t _commmon_choices_show(unsigned long choices, char *buf)
>>> +{
>>> +    int i, len = 0;
>>> +
>>> +    for_each_set_bit(i, &choices, PLATFORM_PROFILE_LAST) {
>>> +        if (len == 0)
>>> +            len += sysfs_emit_at(buf, len, "%s", profile_names[i]);
>>> +        else
>>> +            len += sysfs_emit_at(buf, len, " %s", profile_names[i]);
>>> +    }
>>> +    len += sysfs_emit_at(buf, len, "\n");
>>> +
>>> +    return len;
>>> +}
>>> +
>>> +/**
>>> + * _get_class_choices - Get the available profile choices for a
>>> class device
>>> + * @dev: The class device
>>> + * @choices: Pointer to return the available profile choices
>>> + * Return: The available profile choices
>>> + */
>>> +static int _get_class_choices(struct device *dev, unsigned long
>>> *choices)
>>> +{
>>> +    struct platform_profile_handler *handler;
>>> +    int i;
>>> +
>>> +    lockdep_assert_held(&profile_lock);
>>> +    handler = dev_get_drvdata(dev);
>>> +    for_each_set_bit(i, handler->choices, PLATFORM_PROFILE_LAST)
>>> +        *choices |= BIT(i);
>>
>> Maybe just copying the bitmask would be enough here? In this case we
>> could also drop
>> this function as well.
>
> Right now this could work, but choices and the use of it has gone
> through great lengths to ensure that once there are too many profiles
> it automatically becomes a bigger variable.
>
>     unsigned long choices[BITS_TO_LONGS(PLATFORM_PROFILE_LAST)];
>
> So I would rather keep this as is.
>
I think users of this function can do the locking themself and instead use the functions from bitmap.h. Because _get_class_choices() will break once "choices" becomes bigger.

Thanks,
Armin Wolf

>>
>>> +
>>> +    return 0;
>>> +}
>>> +
>>>   /**
>>>    * name_show - Show the name of the profile handler
>>>    * @dev: The device
>>> @@ -44,9 +84,34 @@ static ssize_t name_show(struct device *dev,
>>>       return -ERESTARTSYS;
>>>   }
>>>
>>> +/**
>>> + * choices_show - Show the available profile choices
>>> + * @dev: The device
>>> + * @attr: The attribute
>>> + * @buf: The buffer to write to
>>> + */
>>> +static ssize_t choices_show(struct device *dev,
>>> +                struct device_attribute *attr,
>>> +                char *buf)
>>> +{
>>> +    unsigned long choices = 0;
>>> +    int err;
>>> +
>>> +    scoped_cond_guard(mutex_intr, return -ERESTARTSYS,
>>> &profile_lock) {
>>> +        err = _get_class_choices(dev, &choices);
>>> +        if (err)
>>> +            return err;
>>> +    }
>>
>> Please directly use the choices field here, no need for a mutex since
>> the choices are static
>> across the lifetime of the platform profile.
>
> But similarly to my other message, the class could be unregistered and
> this needs to be protected.
>
>>
>> Thanks,
>> Armin Wolf
>>
>>> +
>>> +    return _commmon_choices_show(choices, buf);
>>> +}
>>> +
>>>   static DEVICE_ATTR_RO(name);
>>> +static DEVICE_ATTR_RO(choices);
>>> +
>>>   static struct attribute *profile_attrs[] = {
>>>       &dev_attr_name.attr,
>>> +    &dev_attr_choices.attr,
>>>       NULL
>>>   };
>>>   ATTRIBUTE_GROUPS(profile);
>