[Skiboot] [PATCH] opal/hmi: Wakeup the cpu before reading core_fir

[Mahesh Jagannath Salgaonkar]

On 08/20/2018 07:36 PM, Vaibhav Jain wrote:
> When stop state 5 is enabled, reading the core_fir during an HMI can
> result in a xscom read error with xscom_read() returning the
> OPAL_XSCOM_PARTIAL_GOOD error code and core_fir value of all FFs. At
> present this return error code is not handled in decode_core_fir()
> hence the invalid core_fir value is sent to the kernel where it
> interprets it as a FATAL hmi causing a system check-stop.
> 
> This can be prevented by forcing the core to wake-up using before
> reading the core_fir. Hence this patch wraps the call to
> read_core_fir() within calls to dctl_set_special_wakeup() and
> dctl_clear_special_wakeup().
> 
> Suggested-by: Michael Neuling <mikey at neuling.org>
> Signed-off-by: Vaibhav Jain <vaibhav at linux.ibm.com>
> Signed-off-by: Mahesh J Salgaonkar <mahesh at linux.vnet.ibm.com>
> ---
>  core/hmi.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/core/hmi.c b/core/hmi.c
> index 1f665a2f..67c520a0 100644
> --- a/core/hmi.c
> +++ b/core/hmi.c
> @@ -379,7 +379,7 @@ static bool decode_core_fir(struct cpu_thread *cpu,
>  {
>  	uint64_t core_fir;
>  	uint32_t core_id;
> -	int i;
> +	int i, swkup_rc = OPAL_UNSUPPORTED;
>  	bool found = false;
>  	int64_t ret;
>  	const char *loc;
> @@ -390,14 +390,15 @@ static bool decode_core_fir(struct cpu_thread *cpu,
> 
>  	core_id = pir_to_core_id(cpu->pir);
> 
> +	/* Force the core to wakeup, otherwise reading core_fir is unrealiable
> +	 * if stop-state 5 is enabled.

Malfunction Alert is a broadcast HMI and all core should have been
already out of stop state. It is strange that with stop 5 the behaviour
changes. Not sure whether this is a hardware BUG OR stop 5 never wakeup
with HMI.

> +	 */
> +	swkup_rc = dctl_set_special_wakeup(cpu);
> +
>  	/* Get CORE FIR register value. */
>  	ret = read_core_fir(cpu->chip_id, core_id, &core_fir);

May be we should clear special wakeup here once we are done with
reading, instead of doing that in goto out label.

Thanks,
-Mahesh.