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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Fri, Aug 26, 2022 at 03:23:00PM -0500, Stephen Boyd wrote:
> 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).

The affinity setting should not happen since DWC MSI controller doesn't support
setting IRQ affinity (hierarchial IRQ domain). In the migrate_one_irq()
function, there is a check for the existence of the irq_set_affinity()
callback, but the DWC MSI controller return -EINVAL in the callback. So this
is the reason the migration was still atempted?

A quick check would be to test this suspend/resume with GIC ITS for MSI since
it supports settings IRQ affinity and resides in a separate domain.
Chaitanya, can you try that?

> 
> >
> > 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.

Wake up should be handled by a dedicated side-band GPIO or in-band PME message.

But I still wonder how the link stays in L1/L1ss when the clocks are disabled
and PHY is powered down. Maybe the link or phy is powered by a separate power
domain like MX that keeps the link active?

Thanks,
Mani

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