Re: [PATCH v3] ACPI / Processor: add sysfs support for low power idle

["Prakash, Prashanth" <pprakash@codeaurora.org>]

On 11/15/2017 11:37 AM, Rafael J. Wysocki wrote:
> On Wed, Nov 15, 2017 at 7:14 PM, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>
>> On 15/11/17 15:33, Timur Tabi wrote:
>>> On Wed, Nov 8, 2017 at 8:18 AM, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>>> I still prefer this as debugfs and not as sysfs ABI. We already have
>>>> issues with multiple interfaces for the same thing. E.g. cpufreq on x86.
>>>> I don't want this to end up in the same way after few years. CPUIdle
>>>> sysfs should be only sysfs ABI for these, adding an alternative is
>>>> inviting troubles for future especially if some user-space starts using
>>>> it and we will be stuck with that. Moreover with more h/w controlled
>>>> idle we may not provide accurate data sooner.
>>>>
>>>> Sorry for the noise, I will shup up now ;). Since this may be last
>>>> chance to make some noise, I am trying it. I completely understand that
>>>> this is just my opinion and am fine if others thinks it's good to make
>>>> this sysfs ABI.
>>> Unfortunately, I think Prashanth really needs a specific requirement
>>> rather than opinions.
>> I completely understand that. So for I haven't got a solid reason as
>> why debugfs is not sufficient? If it becomes so popular in future, we
>> can discuss and then make it sysfs ABI with more thoughts/discussions.
> Well, the recent discussions regarding tracepoints indicate that the
> ABI rule is not really about where the stuff is located in the
> directory structure. :-)
>
> The main question to me is whether or not the information exposed is
> more suitable for debugfs or for sysfs, considering all of the
> limitations (like one value per file rule in sysfs etc).
>
> Of course, debugfs means that the users of, say, Android will not be
> able to access this information, but should that really influence
> decisions at the technical level?
>
>>> This patch has been languishing for over a month, and we still have
>>> no idea whether it will make 4.15 or if Prashanth is *required* to
>>> make any more changes.
>>>
>> It's sysfs ABI which we need to support for very long time(not in months
>> but in years), so waiting/discussing for couple of months is much safer
>> than spending more time to keep it the sysfs ABI unbroken.
> In either case we need to be sure that the information is exposed the
> way everybody (who cares) likes and there won't be future attempts to
> tweak it to some needs that were not expressed at the outset.
>
> IOW, I'd like more people to look at this and let me know what they think.
>
>> Also I assume(was explicitly mentioned IIRC) that it's purely used
>> for debug and tuning purposes and hence I see *no need* to be part of
>> *sysfs ABI*. Let me know if the circumstances have changed.
> And that is a good argument for putting it into debugs.

Thanks Rafael and Sudeep!

I will take a look at moving this to debugfs.

--
Thanks,
Prashanth