Re: [PATCH v7 2/6] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

[Sudeep Holla]

On 01/07/16 14:07, Daniel Lezcano wrote:
> On 06/28/2016 03:55 PM, Sudeep Holla wrote:
> > ACPI 6.0 introduced an optional object _LPI that provides an alternate
> > method to describe Low Power Idle states. It defines the local power
> > states for each node in a hierarchical processor topology. The OSPM can
> > use _LPI object to select a local power state for each level of processor
> > hierarchy in the system. They used to produce a composite power state
> > request that is presented to the platform by the OSPM.
> >
> > Since multiple processors affect the idle state for any non-leaf
> > hierarchy
> > node, coordination of idle state requests between the processors is
> > required. ACPI supports two different coordination schemes: Platform
> > coordinated and  OS initiated.
> >
> > This patch adds initial support for Platform coordination scheme of LPI.
> >
> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> > ---
>
> Hi Sudeep,
>
> I looked at the acpi processor idle code sometime ago and from my POV,
> it was awful, unnecessary complex and very difficult to maintain. The
> usage of flags all over the places is significant of the lack of control
> of the written code.

So you have any specific things in mind ? That's too broad and I know
it's not so clean, but it's so for legacy reasons. I would leave that
to Rafael to decide as it takes lots of testing to clean up these code.

> Even if you are not responsible of this implementation, the current
> situation forces you to add more awful code on top of that, which is
> clearly against "making Linux better".

OK

> IMO, the current code deserves a huge cleanup before applying anything
> new : cstate and lpi should be investigated to be self-contained in
> their respective file and consolidated, the global variable usage should
> be killed, redundant flag checking removed by recapturing the code flow,
> etc ... I believe the usage of acpi probe table could be one entry point
> to begin this cleanup.

This is not a static table.

--
Regards,
Sudeep