Re: [PATCH v5 2/3] PCI: qcom: Restrict pci transactions after pci suspend

[Stephen Boyd]

Quoting Krishna Chaitanya Chundru (2022-08-25 06:52:43)
>
> On 8/24/2022 10:50 PM, Stephen Boyd wrote:
> > Quoting Krishna Chaitanya Chundru (2022-08-23 20:37:59)
> >> On 8/9/2022 12:42 AM, Stephen Boyd wrote:
> >>> Quoting Krishna chaitanya chundru (2022-08-03 04:28:53)
> >>>> If the endpoint device state is D0 and irq's are not freed, then
> >>>> kernel try to mask interrupts in system suspend path by writing
> >>>> in to the vector table (for MSIX interrupts) and config space (for MSI's).
> >>>>
> >>>> These transactions are initiated in the pm suspend after pcie clocks got
> >>>> disabled as part of platform driver pm  suspend call. Due to it, these
> >>>> transactions are resulting in un-clocked access and eventually to crashes.
> >>> Why are the platform driver pm suspend calls disabling clks that early?
> >>> Can they disable clks in noirq phase, or even later, so that we don't
> >>> have to check if the device is clocking in the irq poking functions?
> >>> It's best to keep irq operations fast, so that irq control is fast given
> >>> that these functions are called from irq flow handlers.
> >> We are registering the pcie pm suspend ops as noirq ops only. And this
> >> msix and config
> >>
> >> access is coming at the later point of time that is reason we added that
> >> check.
> >>
> > What is accessing msix and config? Can you dump_stack() after noirq ops
> > are called and figure out what is trying to access the bus when it is
> > powered down?
>
> The msix and config space is being accessed to mask interrupts. The
> access is coming at the end of the suspend
>
> and near CPU disable. We tried to dump the stack there but the call
> stack is not coming as it is near cpu disable.

That is odd that you can't get a stacktrace.

>
> But we got dump at resume please have look at it
>
> [   54.946268] Enabling non-boot CPUs ...
> [   54.951182] CPU: 1 PID: 21 Comm: cpuhp/1 Not tainted 5.15.41 #105
> 43491e4414b1db8a6f59d56b617b520d92a9498e
> [   54.961122] Hardware name: Qualcomm Technologies, Inc. sc7280 IDP
> SKU2 platform (DT)
> [   54.969088] Call trace:
> [   54.971612]  dump_backtrace+0x0/0x200
> [   54.975399]  show_stack+0x20/0x2c
> [   54.978826]  dump_stack_lvl+0x6c/0x90
> [   54.982614]  dump_stack+0x18/0x38
> [   54.986043]  dw_msi_unmask_irq+0x2c/0x58
> [   54.990096]  irq_enable+0x58/0x90
> [   54.993522]  __irq_startup+0x68/0x94
> [   54.997216]  irq_startup+0xf4/0x140
> [   55.000820]  irq_affinity_online_cpu+0xc8/0x154
> [   55.005491]  cpuhp_invoke_callback+0x19c/0x6e4
> [   55.010077]  cpuhp_thread_fun+0x11c/0x188
> [   55.014216]  smpboot_thread_fn+0x1ac/0x30c
> [   55.018445]  kthread+0x140/0x30c
> [   55.021788]  ret_from_fork+0x10/0x20
> [   55.028243] CPU1 is up
>
> So the same stack should be called at the suspend path while disabling CPU.

Sounds like you're getting hit by affinity changes while offlining CPUs
during suspend (see irq_migrate_all_off_this_cpu()). That will happen
after devices are suspended (all phases of suspend ops).

>
> If there is any other way to remove these calls can you please help us
> point that way.

I'm not sure. I believe genirq assumes the irqchips are always
accessible. There is some support to suspend irqchips. See how the
struct irq_chip::irq_suspend() function is called by syscore ops in the
generic irqchip 'irq_gc_syscore_ops' hooks. Maybe you could add a
syscore suspend/resume hook to disable/enable the clks and power to the
PCI controller. syscore ops run after secondary CPUs are hotplugged out
during suspend.

Or maybe setting the IRQCHIP_MASK_ON_SUSPEND flag can be used so that on
irq migration nothing writes the irq hardware because it is already
masked in the hardware earlier. I think the problem is that on resume
we'll restart the irq from the first CPU online event, when you don't
want to do that because it is too early.

I have another question though, which is do MSIs support wakeup? I don't
see how it works if the whole bus is effectively off during suspend. If
wakeup needs to be supported then I suspect the bus can't be powered
down during suspend.