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

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Message-ID: <22fdc5d1-c082-4e60-a6c9-c67bad295fed@amd.com>
Date: Fri, 8 Nov 2024 13:25:33 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Armin Wolf <W_Armin@....de>, 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

On 11/8/2024 12:06, Armin Wolf wrote:
> 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.
> 

I am thinking it's better to just switch explicitly to an 'unsigned 
long' and add a static check that all profiles fit.  If ever they don't 
fit, the code can be overhauled at that point.

And yes _get_class_choices can go away then, and this is a lot simpler.