Date:	Wed, 19 Jun 2013 21:35:38 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Kevin Hilman <khilman@...aro.org>
CC:	Wolfram Sang <wsa@...-dreams.de>, Tony Lindgren <tony@...mide.com>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-i2c@...r.kernel.org>, Nishanth Menon <nm@...com>
Subject: Re: [PATCH 1/5] i2c: omap: fix spurious IRQs: disable/enable IRQ
 at INTC when idle

On 06/07/2013 11:51 PM, Kevin Hilman wrote:
> Grygorii Strashko <grygorii.strashko@...com> writes:
>
>> From: Kevin Hilman <khilman@...prootsystems.com>
>>
>> Currently, runtime PM is used to keep the device enabled only during
>> active transfers and for a configurable runtime PM autosuspend timout
>> after an xfer.
>>
>> In addition to idling the device, driver's ->runtime_suspend() method
>> currently disables device interrupts when idle.  However, on some SoCs
>> (notably OMAP4+), the I2C hardware may shared with other coprocessors.
>> This means that the MPU will still recieve interrupts if a coprocessor
>> is using the I2C device.  To avoid this, also disable interrupts at
>> the MPU INTC when idling the device in ->runtime_suspend() (and
>> re-enable them in ->runtime_resume().)  This part based on an original
>> patch from Shubhrajyoti Datta.  NOTE: for proper sharing the I2C with
>> a coprocessor, this driver still needs hwspinlock support added.
>>
>> More over, this patch fixes the kernel boot failure which happens when
>> CONFIG_SENSORS_LM75=y:
>>
>> [    2.251220] WARNING: at drivers/bus/omap_l3_noc.c:113 l3_interrupt_handler+0x140/0x184()
>> [    2.257781] L3 custom error: MASTER:MPU TARGET:L4 PER2
>> [    2.264373] Modules linked in:
>> [    2.268463] CPU: 0 PID: 2 Comm: kthreadd Not tainted 3.10.0-rc4-00034-g042dd60-dirty #64
>> [    2.270385] [<c001a80c>] (unwind_backtrace+0x0/0xf0) from [<c0017238>] (show_stack+0x10/0x14)
>> [    2.286102] [<c0017238>] (show_stack+0x10/0x14) from [<c0040fd0>] (warn_slowpath_common+0x4c/0x68)
>> [    2.295593] [<c0040fd0>] (warn_slowpath_common+0x4c/0x68) from [<c0041080>] (warn_slowpath_fmt+0x30/0x40)
>> [    2.299987] [<c0041080>] (warn_slowpath_fmt+0x30/0x40) from [<c02c5ed0>] (l3_interrupt_handler+0x140/0x184)
>> [    2.315582] [<c02c5ed0>] (l3_interrupt_handler+0x140/0x184) from [<c009ffb8>] (handle_irq_event_percpu+0x58/0x258)
>> [    2.323364] [<c009ffb8>] (handle_irq_event_percpu+0x58/0x258) from [<c00a01f4>] (handle_irq_event+0x3c/0x5c)
>> [    2.327819] [<c00a01f4>] (handle_irq_event+0x3c/0x5c) from [<c00a2f7c>] (handle_fasteoi_irq+0xbc/0x164)
>> [    2.337829] [<c00a2f7c>] (handle_fasteoi_irq+0xbc/0x164) from [<c009f978>] (generic_handle_irq+0x20/0x30)
>> [    2.357513] [<c009f978>] (generic_handle_irq+0x20/0x30) from [<c0014168>] (handle_IRQ+0x4c/0xac)
>> [    2.366821] [<c0014168>] (handle_IRQ+0x4c/0xac) from [<c00085b4>] (gic_handle_irq+0x28/0x5c)
>> [    2.375762] [<c00085b4>] (gic_handle_irq+0x28/0x5c) from [<c04f08a4>] (__irq_svc+0x44/0x5c)
>> [    2.379821] Exception stack(0xdb085ec0 to 0xdb085f08)
>> [    2.389953] 5ec0: 00000001 00000001 00000000 db07ea00 40000113 db2317a8 db084000 000002f1
>> [    2.389953] 5ee0: db07ea00 00000000 00000000 00000000 c04fd990 db085f08 c009170c c04f03e8
>> [    2.405609] 5f00: 20000113 ffffffff
>> [    2.408355] [<c04f08a4>] (__irq_svc+0x44/0x5c) from [<c04f03e8>] (_raw_spin_unlock_irqrestore+0x34/0x44)
>> [    2.418304] [<c04f03e8>] (_raw_spin_unlock_irqrestore+0x34/0x44) from [<c00403c0>] (do_fork+0xa4/0x2d4)
>> [    2.427795] [<c00403c0>] (do_fork+0xa4/0x2d4) from [<c0040620>] (kernel_thread+0x30/0x38)
>> [    2.437805] [<c0040620>] (kernel_thread+0x30/0x38) from [<c0063888>] (kthreadd+0xd4/0x13c)
>> [    2.448364] [<c0063888>] (kthreadd+0xd4/0x13c) from [<c0013308>] (ret_from_fork+0x14/0x2c)
>> [    2.448364] ---[ end trace da8cf92c433d1616 ]---
>>
>> The root casue of crash is race between omap_i2c_runtime_suspend()
>>   and omap_i2c_isr_thread()
> If there's a race here, then it's not the same problem which is
> described above, unless the CPU2 IRQ is happening because of a shared
> user of I2C, in which case it doesn't need any additional explanation.
no shared users here
>> CPU1:                                   CPU2:
>> |-omap_i2c_xfer                         |
>>    |- pm_runtime_put_autosuspend()       |
>>       |-timeout                          |-omap_i2c_isr()
>>                                            |-return IRQ_WAKE_THREAD;
>>       |-omap_i2c_runtime_suspend()       |
>>                                          |-omap_i2c_isr_thread()
>>                                            |- oops is here - I2C module is in idle state
> If this is happening, I don't think it's related to $SUBJECT patch (but
> is probably hidden by it.)
I can remove "fix spurious IRQs: " from $SUBJECT. What do you think?
>
> Instead, what probably needs to happen in this is case is that
> omap_i2c_isr() should be doing a "mark last busy" to reset the
> autosuspend timeout.  And, that should be done in a separate patch.
Yes - from one side. From other side, this patch prevents such situation 
to happen.
disable_irq(_dev->irq); - waits for any pending IRQ handlers for this 
interrupt
to complete before returning.

If we are in .runtime_idle() callback - it means I2C transaction has 
been finished
(and It doesn't matter successfully or not) and we don't want to receive 
IRQs any more.

As I mentioned in cover-latter this happens because PM runtime 
auto-suspend isn't
working properly during the boot:

[   23.190002] omap_i2c 48350000.i2c: ==== i2c_add_numbered_adapter
[   23.204681] omap_i2c 48350000.i2c: bus 3 rev0.11 at 400 kHz
[   23.211669] omap_i2c 48350000.i2c: ====== rpm_suspend elapsed 0 last_busy 4294939616
[   23.219879] omap_i2c 48350000.i2c: ====== rpm_suspend expires 4294939716 last_busy 4294939616 autosuspend_delay 1000
[   23.219879] omap_i2c 48350000.i2c: ====== rpm_suspend expires 4294939700
[   23.237274] omap_i2c 48350000.i2c: ====== rpm_suspend mod_timer expires 4294939700
--- the timer scheduled to 84 jiffes
[   23.246185] omap_i2c 48350000.i2c: ==== pm_runtime_put_autosuspend
[   23.253448] omap-dma-engine 4a056000.dma-controller: allocating channel for 62
[   23.261138] omap-dma-engine 4a056000.dma-controller: allocating channel for 61
[   23.269500] omap_i2c 48070000.i2c: ==== omap_i2c_runtime_resume
[   23.275817] omap_i2c 48350000.i2c: ==== omap_i2c_runtime_suspend
--- and expired after ~40 ms

So, there are no guaranty that this race will not happen even if I'll do 
"mark last busy"
in HW IRQ handler (, because in high CPU load use case the threaded IRQ 
can be delayed.

I2C driver should not receive IRQs after finishing the transfer.

>> Cc: Nishanth Menon <nm@...com>
>> Signed-off-by: Kevin Hilman <khilman@...aro.org>
> Both the From: and Signed-off should be from my TI address since the
> work was done while I was working for TI.
>
> Also, if you change the original patch/changelog, you should add a line
> here like:
>
> [grygorii.strashko@...com]: updated changlog
ok.
>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> Kevin

Actually, I can confirm, that this patch really fixes "spurious IRQs" issues
when M3 Ducati is enabled :).

Sorry, for delayed reply - I've had problems with my e-mail.

- grygorii
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