On 5 July 2018 at 13:40, Marc Zyngier [off-list ref] wrote:

On 05/07/18 12:12, Ulf Hansson wrote:

quoted

On 4 July 2018 at 22:29, Marc Zyngier [off-list ref] wrote:

quoted

On Wed, 4 Jul 2018 15:34:36 +0200
Ulf Hansson [off-list ref] wrote:

quoted

On 4 July 2018 at 13:34, Marc Zyngier [off-list ref] wrote:

quoted

On 04/07/18 11:50, Ulf Hansson wrote:

quoted

+ Marc

On 4 July 2018 at 08:28, Stefan Mavrodiev [off-list ref] wrote:

quoted

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.

quoted

quoted

quoted

        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?

quoted

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.

quoted

quoted

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