[PATCH 0/2] cpufreq/opp: rework regulator initialization

[Marek Szyprowski <m.szyprowski@samsung.com>]

Dear All,

Recent commit 9ac6cb5fbb17 ("i2c: add suspended flag and accessors for
i2c adapters") added a visible warning for an attempt to do i2c transfer
over a suspended i2c bus. This revealed a long standing issue in the
cpufreq-dt driver, which gives a following warning during system
suspend/resume cycle:

--->8---
Enabling non-boot CPUs ...
CPU1 is up
CPU2 is up
CPU3 is up
------------[ cut here ]------------
WARNING: CPU: 4 PID: 29 at drivers/i2c/i2c-core-base.c:1869 __i2c_transfer+0x6f8/0xa50
Modules linked in:
CPU: 4 PID: 29 Comm: cpuhp/4 Tainted: G        W         5.0.0-rc4-next-20190131-00024-g54b06b29cc65 #5324
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c01110e8>] (unwind_backtrace) from [<c010d11c>] (show_stack+0x10/0x14)
[<c010d11c>] (show_stack) from [<c09a2584>] (dump_stack+0x90/0xc8)
[<c09a2584>] (dump_stack) from [<c0120bd0>] (__warn+0xf8/0x124)
[<c0120bd0>] (__warn) from [<c0120c3c>] (warn_slowpath_null+0x40/0x48)
[<c0120c3c>] (warn_slowpath_null) from [<c065cda0>] (__i2c_transfer+0x6f8/0xa50)
[<c065cda0>] (__i2c_transfer) from [<c065d168>] (i2c_transfer+0x70/0xe4)
[<c065d168>] (i2c_transfer) from [<c053ce4c>] (regmap_i2c_read+0x48/0x64)
[<c053ce4c>] (regmap_i2c_read) from [<c0536f1c>] (_regmap_raw_read+0xf8/0x450)
[<c0536f1c>] (_regmap_raw_read) from [<c053772c>] (_regmap_bus_read+0x38/0x68)
[<c053772c>] (_regmap_bus_read) from [<c05365a0>] (_regmap_read+0x60/0x250)
[<c05365a0>] (_regmap_read) from [<c05367cc>] (regmap_read+0x3c/0x5c)
[<c05367cc>] (regmap_read) from [<c047cfc0>] (regulator_is_enabled_regmap+0x20/0x90)
[<c047cfc0>] (regulator_is_enabled_regmap) from [<c0477660>] (_regulator_is_enabled+0x34/0x40)
[<c0477660>] (_regulator_is_enabled) from [<c0478674>] (create_regulator+0x1a4/0x25c)
[<c0478674>] (create_regulator) from [<c047c818>] (_regulator_get+0xe4/0x278)
[<c047c818>] (_regulator_get) from [<c068f1dc>] (dev_pm_opp_set_regulators+0xa0/0x1c0)
[<c068f1dc>] (dev_pm_opp_set_regulators) from [<c0698cc8>] (cpufreq_init+0x98/0x2d0)
[<c0698cc8>] (cpufreq_init) from [<c06959e4>] (cpufreq_online+0xc8/0x71c)
[<c06959e4>] (cpufreq_online) from [<c06960fc>] (cpuhp_cpufreq_online+0x8/0x10)
[<c06960fc>] (cpuhp_cpufreq_online) from [<c01213d4>] (cpuhp_invoke_callback+0xf4/0xebc)
[<c01213d4>] (cpuhp_invoke_callback) from [<c0122e4c>] (cpuhp_thread_fun+0x1d8/0x320)
[<c0122e4c>] (cpuhp_thread_fun) from [<c0149858>] (smpboot_thread_fn+0x194/0x340)
[<c0149858>] (smpboot_thread_fn) from [<c014573c>] (kthread+0x124/0x160)
[<c014573c>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20)
Exception stack(0xe897dfb0 to 0xe897dff8)
dfa0:                                     00000000 00000000 00000000 00000000
dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
dfe0: 00000000 00000000 00000000 00000000 00000013 00000000
irq event stamp: 3865
hardirqs last  enabled at (3873): [<c0186dec>] vprintk_emit+0x228/0x2a4
hardirqs last disabled at (3880): [<c0186cf0>] vprintk_emit+0x12c/0x2a4
softirqs last  enabled at (3052): [<c0102564>] __do_softirq+0x3a4/0x66c
softirqs last disabled at (3043): [<c0128464>] irq_exit+0x140/0x168
---[ end trace db48b455d924fec2 ]---
CPU4 is up
CPU5 is up
CPU6 is up
CPU7 is up
--->8---

This is a scenario that triggers the above issue:

1. system disables non-boot cpu's at the end of system suspend procedure,
2. this in turn deinitializes cpufreq drivers for the disabled cpus,
3. early in the system resume procedure all cpus are got back to online
   state,
4. this in turn causes cpufreq to be initialized for the newly onlined
   cpus,
5. cpufreq-dt acquires all its resources (clocks, regulators) during
   ->init() callback,
6. getting regulator require to check its state, what in turn requires
   i2c transfer,
7. during system early resume stage this is not really possible.

The issue is caused by cpufreq-dt driver not keeping its resources for
the whole driver lifetime and relying that they can be always acquired
at any system context. This problem has been observed on Samsung
Exynos based Odroid XU3/XU4 boards, but it happens on all boards, which
have separate regulators for different CPU clusters.

To fix this issue I've rewritten resources (clock and regulators)
handling in cpufreq-dt driver. Now the driver gathers them in its
->probe() and keeps using them until the ->remove() happens. This
required also some rework in common opp regulators handling code.
Namely, regulators are no longer assigned by name, instead the caller
has to pass proper regulator object. The side-effect of this work
is also a removal of the FIXME item and correct handling of deferred
probe caused by lack of non-CPU0 regulator.

Best regards
Marek Szyprowski
Samsung R&D Institute Poland


Patch summary:

Marek Szyprowski (2):
  cpufreq: dt/ti/opp: move regulators initialization to the drivers
  cpufreq: dt: rework resources initialization

 drivers/cpufreq/cpufreq-dt.c | 127 +++++++++++++++--------------------
 drivers/cpufreq/ti-cpufreq.c |  42 ++++++++++--
 drivers/opp/core.c           |  40 ++---------
 include/linux/pm_opp.h       |   2 +-
 4 files changed, 96 insertions(+), 115 deletions(-)

-- 
2.17.1