[PATCH] clk: Manage proper runtime PM state in clk_change_rate()

[Marek Szyprowski]

clk_change_rate() propagates rate change down to all its children. Such
operation requires managing proper runtime PM state of each child, what
was missing. Add needed calls to clk_pm_runtime*() to ensure that
set_rate() clock callback is called on runtime active clock.

This fixes following issue found on Exynos5433 TM2 board with devfreq
enabled:

Synchronous External Abort: synchronous external abort (0x96000210) at 0xffffff80093f5600
Internal error: : 96000210 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 5 Comm: kworker/u16:0 Not tainted 4.15.0-rc1-next-20171129+ #4
Hardware name: Samsung TM2 board (DT)
Workqueue: devfreq_wq devfreq_monitor
task: ffffffc0ca96b600 task.stack: ffffff80093a8000
pstate: a0000085 (NzCv daIf -PAN -UAO)
pc : clk_divider_set_rate+0x54/0x118
lr : clk_divider_set_rate+0x44/0x118
...
Process kworker/u16:0 (pid: 5, stack limit = 0xffffff80093a8000)
Call trace:
 clk_divider_set_rate+0x54/0x118
 clk_change_rate+0xfc/0x4e0
 clk_change_rate+0x1f0/0x4e0
 clk_change_rate+0x1f0/0x4e0
 clk_change_rate+0x1f0/0x4e0
 clk_core_set_rate_nolock+0x138/0x148
 clk_set_rate+0x28/0x50
 exynos_bus_passive_target+0x6c/0x11c
 update_devfreq_passive+0x58/0xb4
 devfreq_passive_notifier_call+0x50/0x5c
 notifier_call_chain+0x4c/0x88
 __srcu_notifier_call_chain+0x54/0x80
 srcu_notifier_call_chain+0x14/0x1c
 update_devfreq+0x100/0x1b4
 devfreq_monitor+0x2c/0x88
 process_one_work+0x148/0x3d8
 worker_thread+0x13c/0x3f8
 kthread+0x100/0x12c
 ret_from_fork+0x10/0x18

Reported-by: Chanwoo Choi <cw00.choi at samsung.com>
Fixes: 9a34b45397e5 ("clk: Add support for runtime PM")
Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
---
For some unknown reason handling of this case was missing in the initial
patch, which added runtime PM support for clock core. Even tests in
linux-next did not revealed this issue. This patch finaly fixes it,
as it is now easy to trigger it with v4.15-rc1.

Best regards
Marek Szyprowski
Samsung R&D Institute Poland
---
 drivers/clk/clk.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 647d056df88c..8a1860a36c77 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1564,6 +1564,9 @@ static void clk_change_rate(struct clk_core *core)
 		best_parent_rate = core->parent->rate;
 	}
 
+	if (clk_pm_runtime_get(core))
+		return;
+
 	if (core->flags & CLK_SET_RATE_UNGATE) {
 		unsigned long flags;
 
@@ -1634,6 +1637,8 @@ static void clk_change_rate(struct clk_core *core)
 	/* handle the new child who might not be in core->children yet */
 	if (core->new_child)
 		clk_change_rate(core->new_child);
+
+	clk_pm_runtime_put(core);
 }
 
 static int clk_core_set_rate_nolock(struct clk_core *core,
-- 
2.15.0