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Subject: Re: [PATCH v3] hwmon: add HP WMI Sensors driver
To:     James Seo <james@equiv.tech>
Cc:     Jean Delvare <jdelvare@suse.com>,
        Guenter Roeck <linux@roeck-us.net>,
        linux-hwmon@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230424100459.41672-1-james@equiv.tech>
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From:   Armin Wolf <W_Armin@gmx.de>
Message-ID: <de4c28c1-6e70-ceb9-484a-143c2b1ebccc@gmx.de>
Date:   Thu, 27 Apr 2023 18:39:33 +0200
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Precedence: bulk

Am 27.04.23 um 09:37 schrieb James Seo:

> On Wed, Apr 26, 2023 at 09:35:33PM +0200, Armin Wolf wrote:
>> Am 26.04.23 um 15:16 schrieb James Seo:
>>
>>> On Mon, Apr 24, 2023 at 11:13:36PM +0200, Armin Wolf wrote:
>>>> Am 24.04.23 um 12:05 schrieb James Seo:
>>>>
>>>>> +	for (i = 0; i < HP_WMI_MAX_INSTANCES; i++, pevents++) {
>>>> Hi,
>>>>
>>>> the WMI driver core already knows how many instances of a given WMI object are available.
>>>> Unfortunately, this information is currently unavailable to drivers. Would it be convenient
>>>> for you to access this information? I could try to implement such a function if needed.
>>>>
>>>>> +	for (i = 0; i < HP_WMI_MAX_INSTANCES; i++, info++) {
>>>> Same as above.
>>>>
>>> Hello,
>>>
>>> Having the WMI object instance count wouldn't make much difference to
>>> me for now. The driver has to iterate through all instances during
>>> init anyway. If I were forced to accommodate 50+ sensors, I'd rewrite
>>> some things and I think I'd want such a function then, but I picked
>>> the current arbitrary limit of 32 because even that seems unlikely.
>>>
>>> So, maybe don't worry about it unless you want to. Or am I missing
>>> something?
>>>
>> Hi,
>>
>> i already have a experimental patch available which adds such a function.
>> If you could test this patch to see if it works, then i could submit it upstream
>> where other drivers could profit from being able to know the number of
>> WMI object instances.
>>
> Both your proposed functions worked as expected.
>
>> Your driver could also profit from such a function, as it could optimize the amount
>> of memory allocated to store WMI object data.
> I suppose I might as well. I assume I'm supposed to wait until your
> new functions are merged before making changes that rely on them?

I think you can submit this driver as-is and provide a follow-up patch once
the changes are merged.

>> The current instance discovery algorithm
>> (using a for-loop and break on error) also has a potential issue: when a single WMI call
>> fails for some reason (ACPI error, ...), all following WMI instances are being ignored.
>>
> This is the intended behavior for now, on the assumption that a real
> ACPI failure probably indicates that the system has bigger problems.
> I do have vague plans to make the driver more tolerant of failure to
> retrieve or validate instances, but haven't decided anything yet.
>
> Regards,
>
> James

Ok.

Armin Wolf