[PATCH v2 0/5] PCI: dwc: improve msi handling

[Marc Zyngier]

On 2020-09-29 14:22, Jon Hunter wrote:
> Hi Jisheng,
> 
> On 29/09/2020 11:48, Jisheng Zhang wrote:
>> Hi Jon,
>> 
>> On Fri, 25 Sep 2020 09:53:45 +0100 Jon Hunter wrote:
>> 
>>> 
>>> On 24/09/2020 12:05, Jisheng Zhang wrote:
>>>> Improve the msi code:
>>>> 1. Add proper error handling.
>>>> 2. Move dw_pcie_msi_init() from each users to designware host to 
>>>> solve
>>>> msi page leakage in resume path.
>>> 
>>> Apologies if this is slightly off topic, but I have been meaning to 
>>> ask
>>> about MSIs and PCI. On Tegra194 which uses the DWC PCI driver, 
>>> whenever we
>>> hotplug CPUs we see the following warnings ...
>>> 
>>>  [      79.068351] WARNING KERN IRQ70: set affinity failed(-22).
>>>  [      79.068362] WARNING KERN IRQ71: set affinity failed(-22).
>>> 
>> 
>> I tried to reproduce this issue on Synaptics SoC, but can't reproduce 
>> it.
>> Per my understanding of the code in kernel/irq/cpuhotplug.c, this 
>> warning
>> happened when we migrate irqs away from the offline cpu, this 
>> implicitly
>> implies that before this point the irq has bind to the offline cpu, 
>> but how
>> could this happen given current dw_pci_msi_set_affinity() 
>> implementation
>> always return -EINVAL
> 
> By default the smp_affinity should be set so that all CPUs can be
> interrupted ...
> 
> $ cat /proc/irq/70/smp_affinity
> 0xff
> 
> In my case there are 8 CPUs and so 0xff implies that the interrupt can
> be triggered on any of the 8 CPUs.
> 
> Do you see the set_affinity callback being called for the DWC irqchip 
> in
> migrate_one_irq()?

The problem is common to all MSI implementations that end up muxing
all the end-point MSIs into a single interrupt. With these systems,
you cannot set the affinity of individual MSIs (they don't target a
CPU, they target another interrupt... braindead). Only the mux
interrupt can have its affinity changed.

So returning -EINVAL is the right thing to do.

          M.
-- 
Jazz is not dead. It just smells funny...