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Re: Fix preempt-rt on AT91

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  Re: Fix preempt-rt on AT91 Alexandre Belloni <alexandre.belloni@free-electrons.com> - 2016-03-05 12:40 +0100
    Re: Fix preempt-rt on AT91 Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-03-08 12:10 +0100
      Re: Fix preempt-rt on AT91 Thomas Gleixner <tglx@linutronix.de> - 2016-03-08 12:30 +0100
      Re: Fix preempt-rt on AT91 Alexandre Belloni <alexandre.belloni@free-electrons.com> - 2016-03-08 19:40 +0100
        arm: at91: do not disable/enable clocks in a row Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-03-09 11:00 +0100

#1350870 — Re: Fix preempt-rt on AT91

Hi Sebastian,

On 18/01/2016 at 18:42:59 +0100, Sebastian Andrzej Siewior wrote :
> > 3/ Finally, the kernel will crash when initializing the PMC driver. This is
> > solved by this series that will hopefully land in the mainline:
> >   http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/390954.html
> 
> This is new, isn't it? So the series in currently in v3 and people seem
> happy with it. Please poke me once with the commit ids once it is merged
> on its way upstream and I will try cherry-pick them from next or so.
> 

The series landed in arm-soc and is making its way to v4.6. I guess you
can pull the original pull request. It is based on v4.5-rc1 but should
apply cleanly on v4.4:

The following changes since commit
92e963f50fc74041b5e9e744c330dca48e04f08d:

  Linux 4.5-rc1 (2016-01-24 13:06:47 -0800)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git
tags/at91-ab-4.6-drivers

for you to fetch changes up to 0002ca168f16e5b6ac67415a4e0198cc39af2b7f:

  clk: at91: remove useless includes (2016-02-17 17:53:04 +0100)




You may also stop at 99a81706526fb167029a940ef1f7bfbe882abd3e which
should solve the crash but it has not been tested as thoroughly.

Thanks!

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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#1352880

* Alexandre Belloni | 2016-03-05 12:35:53 [+0100]:

>Hi Sebastian,
Hi Alexandre,

>The series landed in arm-soc and is making its way to v4.6. I guess you
>can pull the original pull request. It is based on v4.5-rc1 but should
>apply cleanly on v4.4:

I sucked this in. It seems to work. What remains that free_irq() thingy:
|WARNING: CPU: 0 PID: 0 at kernel/irq/manage.c:1541 __free_irq+0xb4/0x2e0()
|Trying to free already-free IRQ 16
|CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.4-rt10+ #219
|Hardware name: Atmel SAMA5
|[<c0015bd0>] (unwind_backtrace) from [<c0013604>] (show_stack+0x10/0x14)
|[<c0013604>] (show_stack) from [<c002b850>] (warn_slowpath_common+0x80/0xac)
|[<c002b850>] (warn_slowpath_common) from [<c002b8ac>] (warn_slowpath_fmt+0x30/0x40)
|[<c002b8ac>] (warn_slowpath_fmt) from [<c005adfc>] (__free_irq+0xb4/0x2e0)
|[<c005adfc>] (__free_irq) from [<c005b0a0>] (free_irq+0x30/0x4c)
|[<c005b0a0>] (free_irq) from [<c0429034>] (pit_clkevt_shutdown+0x24/0x2c)
|[<c0429034>] (pit_clkevt_shutdown) from [<c0076430>] (clockevents_switch_state+0x60/0x130)
|---[ end trace 0000000000000001 ]---

which is a different problem and was there. The new thing is this:

|WARNING: CPU: 0 PID: 1 at kernel/locking/rtmutex.c:2062 rt_mutex_trylock+0x30/0x108)
|Modules linked in:
|CPU: 0 PID: 1 Comm: swapper Tainted: G        W       4.4.4-rt10+ #219
|Hardware name: Atmel SAMA5
|[<c0015bd0>] (unwind_backtrace) from [<c0013604>] (show_stack+0x10/0x14)
|[<c0013604>] (show_stack) from [<c002b850>] (warn_slowpath_common+0x80/0xac)
|[<c002b850>] (warn_slowpath_common) from [<c002b918>] (warn_slowpath_null+0x1c/0x24)
|[<c002b918>] (warn_slowpath_null) from [<c054a54c>] (rt_mutex_trylock+0x30/0x108)
|[<c054a54c>] (rt_mutex_trylock) from [<c054bd0c>] (rt_spin_trylock_irqsave+0x10/0x1c)
|[<c054bd0c>] (rt_spin_trylock_irqsave) from [<c043e030>] (clk_enable_lock+0x18/0x114)
|[<c043e030>] (clk_enable_lock) from [<c043f600>] (clk_disable+0x1c/0x34)
|[<c043f600>] (clk_disable) from [<c0429188>] (tc_shutdown+0x34/0x3c)
|[<c0429188>] (tc_shutdown) from [<c04291b0>] (tc_set_oneshot+0x20/0x50)
|[<c04291b0>] (tc_set_oneshot) from [<c00764a4>] (clockevents_switch_state+0xd4/0x130)
|[<c00764a4>] (clockevents_switch_state) from [<c00773e8>] (tick_switch_to_oneshot+0x48/0xb8)
|[<c00773e8>] (tick_switch_to_oneshot) from [<c006a480>] (hrtimer_run_queues+0x48/0x108)
|[<c006a480>] (hrtimer_run_queues) from [<c0068dd8>] (update_process_times+0x2c/0x64)
|[<c0068dd8>] (update_process_times) from [<c0076ad0>] (tick_handle_periodic+0x1c/0x90)
|[<c0076ad0>] (tick_handle_periodic) from [<c0429274>] (ch2_irq+0x20/0x28)
|[<c0429274>] (ch2_irq) from [<c005a39c>] (handle_irq_event_percpu+0x74/0x16c)

Is it possible to drop this disable/enable clock on the switch from pit
to one shot mode?

>You may also stop at 99a81706526fb167029a940ef1f7bfbe882abd3e which
>should solve the crash but it has not been tested as thoroughly.

Did you confuse the sha1 with something? This patch is called ("clk:
at91: remove IRQ handling and use polling") and is part of the series
you gave (patch #3).

>Thanks!

Sebastian

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#1352901

On Tue, 8 Mar 2016, Sebastian Andrzej Siewior wrote:
> I sucked this in. It seems to work. What remains that free_irq() thingy:
> |WARNING: CPU: 0 PID: 0 at kernel/irq/manage.c:1541 __free_irq+0xb4/0x2e0()
> |Trying to free already-free IRQ 16
> |CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.4-rt10+ #219
> |Hardware name: Atmel SAMA5
> |[<c0015bd0>] (unwind_backtrace) from [<c0013604>] (show_stack+0x10/0x14)
> |[<c0013604>] (show_stack) from [<c002b850>] (warn_slowpath_common+0x80/0xac)
> |[<c002b850>] (warn_slowpath_common) from [<c002b8ac>] (warn_slowpath_fmt+0x30/0x40)
> |[<c002b8ac>] (warn_slowpath_fmt) from [<c005adfc>] (__free_irq+0xb4/0x2e0)
> |[<c005adfc>] (__free_irq) from [<c005b0a0>] (free_irq+0x30/0x4c)
> |[<c005b0a0>] (free_irq) from [<c0429034>] (pit_clkevt_shutdown+0x24/0x2c)
> |[<c0429034>] (pit_clkevt_shutdown) from [<c0076430>] (clockevents_switch_state+0x60/0x130)
> |---[ end trace 0000000000000001 ]---
> 
> which is a different problem and was there. The new thing is this:

I think we really need to have this irq_en/disable_action() thingy sooner than
later.

> Is it possible to drop this disable/enable clock on the switch from pit
> to one shot mode?

There was an earlier discussion about the clk stuff. Actually the lock
protecting disable/enable should be made raw, but there was some crap going on
in some of the clk callbacks which made that impossible. We realy should
revisit this.

Thanks,

	tglx

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#1353306

Hi,

On 08/03/2016 at 12:06:39 +0100, Sebastian Andrzej Siewior wrote :
> I sucked this in. It seems to work. What remains that free_irq() thingy:
> |WARNING: CPU: 0 PID: 0 at kernel/irq/manage.c:1541 __free_irq+0xb4/0x2e0()
> |Trying to free already-free IRQ 16
> |CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.4-rt10+ #219
> |Hardware name: Atmel SAMA5
> |[<c0015bd0>] (unwind_backtrace) from [<c0013604>] (show_stack+0x10/0x14)
> |[<c0013604>] (show_stack) from [<c002b850>] (warn_slowpath_common+0x80/0xac)
> |[<c002b850>] (warn_slowpath_common) from [<c002b8ac>] (warn_slowpath_fmt+0x30/0x40)
> |[<c002b8ac>] (warn_slowpath_fmt) from [<c005adfc>] (__free_irq+0xb4/0x2e0)
> |[<c005adfc>] (__free_irq) from [<c005b0a0>] (free_irq+0x30/0x4c)
> |[<c005b0a0>] (free_irq) from [<c0429034>] (pit_clkevt_shutdown+0x24/0x2c)
> |[<c0429034>] (pit_clkevt_shutdown) from [<c0076430>] (clockevents_switch_state+0x60/0x130)
> |---[ end trace 0000000000000001 ]---
> 
> which is a different problem and was there. The new thing is this:
> 
> |WARNING: CPU: 0 PID: 1 at kernel/locking/rtmutex.c:2062 rt_mutex_trylock+0x30/0x108)
> |Modules linked in:
> |CPU: 0 PID: 1 Comm: swapper Tainted: G        W       4.4.4-rt10+ #219
> |Hardware name: Atmel SAMA5
> |[<c0015bd0>] (unwind_backtrace) from [<c0013604>] (show_stack+0x10/0x14)
> |[<c0013604>] (show_stack) from [<c002b850>] (warn_slowpath_common+0x80/0xac)
> |[<c002b850>] (warn_slowpath_common) from [<c002b918>] (warn_slowpath_null+0x1c/0x24)
> |[<c002b918>] (warn_slowpath_null) from [<c054a54c>] (rt_mutex_trylock+0x30/0x108)
> |[<c054a54c>] (rt_mutex_trylock) from [<c054bd0c>] (rt_spin_trylock_irqsave+0x10/0x1c)
> |[<c054bd0c>] (rt_spin_trylock_irqsave) from [<c043e030>] (clk_enable_lock+0x18/0x114)
> |[<c043e030>] (clk_enable_lock) from [<c043f600>] (clk_disable+0x1c/0x34)
> |[<c043f600>] (clk_disable) from [<c0429188>] (tc_shutdown+0x34/0x3c)
> |[<c0429188>] (tc_shutdown) from [<c04291b0>] (tc_set_oneshot+0x20/0x50)
> |[<c04291b0>] (tc_set_oneshot) from [<c00764a4>] (clockevents_switch_state+0xd4/0x130)
> |[<c00764a4>] (clockevents_switch_state) from [<c00773e8>] (tick_switch_to_oneshot+0x48/0xb8)
> |[<c00773e8>] (tick_switch_to_oneshot) from [<c006a480>] (hrtimer_run_queues+0x48/0x108)
> |[<c006a480>] (hrtimer_run_queues) from [<c0068dd8>] (update_process_times+0x2c/0x64)
> |[<c0068dd8>] (update_process_times) from [<c0076ad0>] (tick_handle_periodic+0x1c/0x90)
> |[<c0076ad0>] (tick_handle_periodic) from [<c0429274>] (ch2_irq+0x20/0x28)
> |[<c0429274>] (ch2_irq) from [<c005a39c>] (handle_irq_event_percpu+0x74/0x16c)
> 
> Is it possible to drop this disable/enable clock on the switch from pit
> to one shot mode?
> 

Both are things to work on. In the mean time, I'm using the following
patch:
https://github.com/alexandrebelloni/linux/commit/3a2eae463fce18ae815b887a5c9ca1a657b180ac

I understood from
http://lkml.iu.edu/hypermail/linux/kernel/1601.2/00941.html that this
was not your preferred course of action.

Even if that is something that is only seen when using preempt-rt, that
is probably something I should push mainline.

> >You may also stop at 99a81706526fb167029a940ef1f7bfbe882abd3e which
> >should solve the crash but it has not been tested as thoroughly.
> 
> Did you confuse the sha1 with something? This patch is called ("clk:
> at91: remove IRQ handling and use polling") and is part of the series
> you gave (patch #3).
> 

Yeah, what I meant is that you could stop merging after that patch as
this is the one solving the crash.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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#1353930 — arm: at91: do not disable/enable clocks in a row

* Alexandre Belloni | 2016-03-08 19:39:10 [+0100]:

>Hi,
Hi,

>Both are things to work on. In the mean time, I'm using the following
>patch:
>https://github.com/alexandrebelloni/linux/commit/3a2eae463fce18ae815b887a5c9ca1a657b180ac
>
>I understood from
>http://lkml.iu.edu/hypermail/linux/kernel/1601.2/00941.html that this
>was not your preferred course of action.

That was one thing.  What about this:

---

Currently the driver will disable the clock and enable it one line later
if it is switching from periodic mode into one shot.
This can be avoided and causes a needless warning on -RT.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/clocksource/tcb_clksrc.c |   33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

--- a/drivers/clocksource/tcb_clksrc.c
+++ b/drivers/clocksource/tcb_clksrc.c
@@ -74,6 +74,7 @@ static struct clocksource clksrc = {
 struct tc_clkevt_device {
 	struct clock_event_device	clkevt;
 	struct clk			*clk;
+	bool				clk_enabled;
 	void __iomem			*regs;
 };
 
@@ -91,6 +92,24 @@ static struct tc_clkevt_device *to_tc_cl
  */
 static u32 timer_clock;
 
+static void tc_clk_disable(struct clock_event_device *d)
+{
+	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
+
+	clk_disable(tcd->clk);
+	tcd->clk_enabled = false;
+}
+
+static void tc_clk_enable(struct clock_event_device *d)
+{
+	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
+
+	if (tcd->clk_enabled)
+		return;
+	clk_enable(tcd->clk);
+	tcd->clk_enabled = true;
+}
+
 static int tc_shutdown(struct clock_event_device *d)
 {
 	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
@@ -98,8 +117,14 @@ static int tc_shutdown(struct clock_even
 
 	__raw_writel(0xff, regs + ATMEL_TC_REG(2, IDR));
 	__raw_writel(ATMEL_TC_CLKDIS, regs + ATMEL_TC_REG(2, CCR));
+	return 0;
+}
+
+static int tc_shutdown_clk_off(struct clock_event_device *d)
+{
+	tc_shutdown(d);
 	if (!clockevent_state_detached(d))
-		clk_disable(tcd->clk);
+		tc_clk_disable(d);
 
 	return 0;
 }
@@ -112,7 +137,7 @@ static int tc_set_oneshot(struct clock_e
 	if (clockevent_state_oneshot(d) || clockevent_state_periodic(d))
 		tc_shutdown(d);
 
-	clk_enable(tcd->clk);
+	tc_clk_enable(d);
 
 	/* slow clock, count up to RC, then irq and stop */
 	__raw_writel(timer_clock | ATMEL_TC_CPCSTOP | ATMEL_TC_WAVE |
@@ -134,7 +159,7 @@ static int tc_set_periodic(struct clock_
 	/* By not making the gentime core emulate periodic mode on top
 	 * of oneshot, we get lower overhead and improved accuracy.
 	 */
-	clk_enable(tcd->clk);
+	tc_clk_enable(d);
 
 	/* slow clock, count up to RC, then irq and restart */
 	__raw_writel(timer_clock | ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO,
@@ -168,7 +193,7 @@ static struct tc_clkevt_device clkevt =
 		/* Should be lower than at91rm9200's system timer */
 		.rating			= 125,
 		.set_next_event		= tc_next_event,
-		.set_state_shutdown	= tc_shutdown,
+		.set_state_shutdown	= tc_shutdown_clk_off,
 		.set_state_periodic	= tc_set_periodic,
 		.set_state_oneshot	= tc_set_oneshot,
 	},

Sebastian

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