linux-kernel - [PATCH] fix sysfs showing the correct C-states after AC->DC and DC->AC transitions

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Date:	Wed, 01 Apr 2015 20:04:34 +0200
From:	Thomas Schlichter <thomas.schlichter@....de>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Len Brown <lenb@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: [PATCH] fix sysfs showing the correct C-states after AC->DC and DC->AC transitions

Hello,

I do have a Samsung NC20 netbook which provides the C-states C1 and C2 to the 
OS when connected to AC, and additionally provides the C3 C-state when 
disconnected from AC. With the current kernels I have these two problems 
(regressions):

1. The number of C-states shown in sysfs is fixed to the number of C-states
   present at boot.
   If I boot with AC connected, I always only see the C-states up to C2 even
   if I disconnect AC.

   The reason is commit 130a5f692425e6237229598a8624da0a247f33d5
   "ACPI / cpuidle: remove dev->state_count setting". It removes the update of
   dev->state_count, but sysfs uses exactly this variable to show the
   C-states.

   The fix is to use drv->state_count in sysfs. As this is currently the last
   user of dev->state_count, this variable can be completely removed. And this
   is exactly what Bartlomiej Zolnierkiewicz's not yet applied patch "[PATCH
   v2 9/9] cpuidle: remove state_count field from struct cpuidle_device"
   http://marc.info/?m=138756533317836 does.

   Long story short: That patch fixes problem 1 for me.

2. After a AC->DC or DC->AC transition, the name and description of the
   POLLING C-state become "<null>".

   Here, the reason is commit d7c7f103262bc2248548ed0e113e916e843c4eeb
   "cpuidle: don't call poll_idle_init() for every cpu". It only calls
   poll_idle_init() during cpuidle_register_driver() instead of
   cpuidle_enable_device() and thus does not re-initialize the fields of
   drv->states[0] after acpi_processor_setup_cpuidle_states() cleared them.

   Here, the fix is to _not_ clear drv->states[0] in
   acpi_processor_setup_cpuidle_states(). For this purpose I created a small
   patch.

For your convenience, both of the fixing patches are attached to this mail.
The first one is necessary for all kernels since 3.14, the second one for all
kernels since 3.13. So I'd propose to push both of them also to the necessary
stable kernels.

Kind regards,
  Thomas
View attachment "0001-cpuidle-remove-state_count-field-from-struct-cpuidle.patch" of type "text/x-patch" (2353 bytes)

View attachment "0002-ACPI-cpuidle-do-not-overwrite-name-and-description-o.patch" of type "text/x-patch" (1290 bytes)