linux-kernel - Re: [PATCH v13 09/12] ACPI: x86: s2idle: Add a function to get constraints for a device

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Date:   Fri, 18 Aug 2023 09:04:31 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Iain Lane <iain@...ngesquash.org.uk>,
        Shyam-sundar S-k <Shyam-sundar.S-k@....com>
Subject: Re: [PATCH v13 09/12] ACPI: x86: s2idle: Add a function to get
 constraints for a device

On 8/18/2023 05:47, Andy Shevchenko wrote:
> On Fri, Aug 18, 2023 at 10:31:03AM +0200, Rafael J. Wysocki wrote:
>> On Fri, Aug 18, 2023 at 7:15 AM Mario Limonciello
>> <mario.limonciello@....com> wrote:
> 
> ...
> 
>>> +int acpi_get_lps0_constraint(struct device *dev)
>>
>> I think that some overhead would be reduced below if this were taking
>> a struct acpi_device pointer as the argument.
> 
> Hmm... Either you need a pointer to handle, which involves pointer arithmetics
> or something else. I would believe if you tell that ACPI handle should be passed,
> but current suggestion is not obvious to me how it may help.

To Rafael's point about overhead there are potentially "less" calls into 
acpi_get_lps0_constraint if it's a 'struct acpi_device' pointer because 
it won't be called by caller for any devices that don't have an ACPI 
companion.

> 
>>> +{
>>> +       struct lpi_constraints *entry;
>>> +
>>> +       for_each_lpi_constraint(entry) {
>>> +               if (!device_match_acpi_handle(dev, entry->handle))
> 
> Here we retrieve handle...
> 
>>> +                       continue;
>>> +               acpi_handle_debug(entry->handle,
>>> +                                 "ACPI device constraint: %d\n", entry->min_dstate);
>>> +               return entry->min_dstate;
>>> +       }
> 
>>> +       dev_dbg(dev, "No ACPI device constraint specified\n");
> 
> ...and here we are using dev directly (otherwise acpi_handle_dbg() should be used).

I'll just move the debugging statements into the caller of 
acpi_get_lps0_constraint().

> 
>>> +       return -ENODEV;
>>
>> ACPI_STATE_UNKNOWN?

Much better, thanks.

>>
>>> +}
>