[PATCH] powerpc/rtas: Introduce rtas_get_sensor_nonblocking() for pci hotplug driver.

[Mahesh J Salgaonkar]

On 2021-11-29 22:53:41 Mon, Nathan Lynch wrote:
> Mahesh Salgaonkar <mahesh at linux.ibm.com> writes:
> > When certain PHB HW failure causes phyp to recover PHB, it marks the PE
> > state as temporarily unavailable until recovery is complete. This also
> > triggers an EEH handler in Linux which needs to notify drivers, and perform
> > recovery. But before notifying the driver about the pci error it uses
> > get_adapter_state()->get-sesnor-state() operation of the hotplug_slot to
> > determine if the slot contains a device or not. if the slot is empty, the
> > recovery is skipped entirely.
> >
> > However on certain PHB failures, the rtas call get-sesnor-state() returns
> > extended busy error (9902) until PHB is recovered by phyp. Once PHB is
> > recovered, the get-sensor-state() returns success with correct presence
> > status. The rtas call interface rtas_get_sensor() loops over the rtas call
> > on extended delay return code (9902) until the return value is either
> > success (0) or error (-1). This causes the EEH handler to get stuck for ~6
> > seconds before it could notify that the pci error has been detected and
> > stop any active operations.
> 
> I am curious whether you see any difference with "powerpc/rtas:
> rtas_busy_delay() improvements" which was recently applied. It will
> cause the the calling task to sleep in response to a 990x status instead
> of immediately retrying:
> 
> https://git.kernel.org/powerpc/c/38f7b7067dae0c101be573106018e8af22a90fdf
> 
> If that commit helps then maybe this change isn't needed.

I tried with above commit but it didn't help.

> 
> Maybe it would be better to have rpaphp_get_sensor_state() invoke
> rtas_call("get-sensor-state", ...) directly and code whatever special
> behavior is needed there, instead of introducing a new exported API. The

Posted v3 with above approach.
https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-December/237538.html

Thanks for your review.
-Mahesh.

-- 
Mahesh J Salgaonkar