Re: [PATCH v2 1/1] mmc: sunxi: Disable irq during pm_suspend

[Ulf Hansson <ulf.hansson@linaro.org>]

On 5 July 2018 at 13:40, Marc Zyngier <marc.zyngier@arm.com> wrote:
> On 05/07/18 12:12, Ulf Hansson wrote:
>> On 4 July 2018 at 22:29, Marc Zyngier <marc.zyngier@arm.com> wrote:
>>> On Wed, 4 Jul 2018 15:34:36 +0200
>>> Ulf Hansson <ulf.hansson@linaro.org> wrote:
>>>
>>>> On 4 July 2018 at 13:34, Marc Zyngier <marc.zyngier@arm.com> wrote:
>>>>> On 04/07/18 11:50, Ulf Hansson wrote:
>>>>>> + Marc
>>>>>>
>>>>>> On 4 July 2018 at 08:28, Stefan Mavrodiev <stefan@olimex.com> wrote:
>>>>>>> When mmc host controller enters suspend state, the clocks are
>>>>>>> disabled, but irqs are not. For some reason the irqchip emits
>>>>>>> false interrupts, which causes system lock loop.
>>>>>>>
>>>>>>> Debug log is:
>>>>>>>   ...
>>>>>>>   sunxi-mmc 1c11000.mmc: setting clk to 52000000, rounded 51200000
>>>>>>>   sunxi-mmc 1c11000.mmc: enabling the clock
>>>>>>>   sunxi-mmc 1c11000.mmc: cmd 13(8000014d) arg 10000 ie 0x0000bbc6 len 0
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00000004 idi 00000000
>>>>>>>   sunxi-mmc 1c11000.mmc: cmd 6(80000146) arg 3210101 ie 0x0000bbc6 len 0
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00000004 idi 00000000
>>>>>>>   sunxi-mmc 1c11000.mmc: cmd 13(8000014d) arg 10000 ie 0x0000bbc6 len 0
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00000004 idi 00000000
>>>>>>>   mmc1: new DDR MMC card at address 0001
>>>>>>>   mmcblk1: mmc1:0001 AGND3R 14.6 GiB
>>>>>>>   mmcblk1boot0: mmc1:0001 AGND3R partition 1 4.00 MiB
>>>>>>>   mmcblk1boot1: mmc1:0001 AGND3R partition 2 4.00 MiB
>>>>>>>   sunxi-mmc 1c11000.mmc: cmd 18(80003352) arg 0 ie 0x0000fbc2 len 409
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00004000 idi 00000002
>>>>>>>    mmcblk1: p1
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
>>>>>>>   sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
>>>>>>> and so on...
>>>>>>>
>>>>>>> This issue apears on eMMC cards, routed on MMC2 slot. The patch is
>>>>>>> tested with A20-OLinuXino-MICRO/LIME/LIME2 boards.
>>>>>>>
>>>>>>> Fixes: 9a8e1e8cc2c0 ("mmc: sunxi: Add runtime_pm support")
>>>>>>> Signed-off-by: Stefan Mavrodiev <stefan@olimex.com>
>>>>>>> ---
>>>>>>>  Changes in v2:
>>>>>>>   - Add comment why disable_irq() is necessary
>>>>>>>
>>>>>>> ---
>>>>>>>  drivers/mmc/host/sunxi-mmc.c | 7 +++++++
>>>>>>>  1 file changed, 7 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
>>>>>>> index e747259..8e7f3e3 100644
>>>>>>> --- a/drivers/mmc/host/sunxi-mmc.c
>>>>>>> +++ b/drivers/mmc/host/sunxi-mmc.c
>>>>>>> @@ -1446,6 +1446,7 @@ static int sunxi_mmc_runtime_resume(struct device *dev)
>>>>>>>         sunxi_mmc_init_host(host);
>>>>>>>         sunxi_mmc_set_bus_width(host, mmc->ios.bus_width);
>>>>>>>         sunxi_mmc_set_clk(host, &mmc->ios);
>>>>>>> +       enable_irq(host->irq);
>>>>>>>
>>>>>>>         return 0;
>>>>>>>  }
>>>>>>> @@ -1455,6 +1456,12 @@ static int sunxi_mmc_runtime_suspend(struct device *dev)
>>>>>>>         struct mmc_host *mmc = dev_get_drvdata(dev);
>>>>>>>         struct sunxi_mmc_host *host = mmc_priv(mmc);
>>>>>>>
>>>>>>> +       /*
>>>>>>> +        * When clocks are off, it's possible receiving
>>>>>>> +        * fake interrupts, which will stall the system.
>>>>>>> +        * Disabling the irq  will prevent this.
>>>>>>> +        */
>>>>>>> +       disable_irq(host->irq);
>>>>>>
>>>>>> No, this doesn't work for shared IRQs.
>>>>>
>>>>> Well, in this case, it does work, because that interrupt line cannot be
>>>>> shared with anything else, if I understand how the SoC is wired: each
>>>>> MMC controller has a dedicated interrupt line to the GIC, and it isn't
>>>>> shared with anything (that's on the A20 though, and I don't know about
>>>>> other SoCs integrating the same IP).
>>>>
>>>> That's the problem. This may work on some SoCs but not on others.
>>>>
>>>>>
>>>>>>
>>>>>>>         sunxi_mmc_reset_host(host);
>>>>>>>         sunxi_mmc_disable(host);
>>>>>>>
>>>>>>> --
>>>>>>> 2.7.4
>>>>>>>
>>>>>>
>>>>>> The only option today is to use free_irq() in runtime suspend and then
>>>>>> re-request the irq to re-install the handler at runtime resume.
>>>>>>
>>>>>> That's not an optimal solution, which is pointed out in the below
>>>>>> discussion as well. Moreover, it has also turned out using free_irq()
>>>>>> is also problematic in cases threaded handlers are used.
>>>>>>
>>>>>> Here's the link to the discussion, it's not the only one I know of, so
>>>>>> this is common problem.
>>>>>> https://lkml.org/lkml/2016/1/28/213
>>>>>>
>>>>>> Care to have a hack on the "common" solution, which in principle means
>>>>>> adding APIs to genirq that can disable/enable handlers from being
>>>>>> called, rather than the entire IRQ line.
>>>>>
>>>>> That doesn't work. You still end-up with a screaming interrupt, and you
>>>>> will still spend 100% of your time in interrupt context for nothing.
>>>>>
>>>>> Eventually, the kernel will have enough (the /other/ shared handlers
>>>>> returning IRQ_NONE all the time), and will forcefully kill that
>>>>> particular interrupt interrupt line, meaning you end-up in the same
>>>>> situation of having the line disabled for all the users of that
>>>>> interrupt line. Except that now, it is disabled forever.
>>>>
>>>> Ahh, correct!
>>>>
>>>> Sounds like free_irq() is what we need. Only that it's bit heavy
>>>> weight as we need to re-install handlers.
>>>
>>> BTW, free_irq() doesn't help you either in the case of a shared
>>> handler. You'll end-up in the exact same scenario as above.
>>
>> In regards to the spurious interrupt storm issue, yes, I fully agree.
>>
>> On the other hand, in case of a shared IRQ, don't we want the genirq
>> core to deal with disabling the IRQ, rather than the driver?
>
> How do you propose we do that? You have an OR gate between two device,
> and the result of that gate is directly plugged in the interrupt controller.
>
> The only thing the genirq subsystem can do is take the interrupt. If
> nobody cares, the whole interrupt *line* will eventually get disabled.

Yep, something like that. That would work, right?

>
>> Also, don't forget the other related issue, which is when the IRQ
>> handler gets invoked (not as a storm, but once is enough), either
>> because of a spurious IRQ or because of a shared IRQ - while the
>> device is in a low power state (runtime suspended with clock gated for
>> example). If that happens and the handler accesses a register the
>> handler may hang.
>
> Doing a free_irq() in that case is fine, as long as the rate of spurious
> interrupts is low.

Yep.

>
>>> The real solution to this is to prevent the device itself from
>>> generating interrupts (or to forbid interrupt sharing if it isn't
>>> possible).
>>
>> I fully agree that the device should be configured to not deliver
>> interrupt, this is the first and most important step a driver should
>> take. For example it should mask its device's IRQ register bits.
>>
>> However, this isn't sufficient, because of shared IRQs and buggy HWs
>> delivering spurious IRQs.
>
> It *is* sufficient for shared IRQs. Actually, it is the only way to
> sanely implement shared IRQs (you must gate the interrupt upstream of
> the summing interrupt controller). Buggy HW is another story (and that's
> probably the case here).
>
> Now: can we please get this patch merged? ;-)

Right, I have applied it for fixes!

Thanks for the discussion! However it would be nice to reach a
conclusion for the problem generically.

disable|enable_irq() only works for the non-shared IRQs.

Kind regards
Uffe