[Skiboot] [PATCH 3/3] xscom: Do not wait indefinitely for xscom operation to complete

[Nicholas Piggin]

Excerpts from Vasant Hegde's message of May 20, 2020 9:51 pm:
> In some corner cases (specially on P8), xscom_wait_done() won't
> complete.. resulting in waiting forever.
> 
> This patch retries for predefined time and then exits even if xscom
> operation did not complete.
> 
> Signed-off-by: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>
> ---
>  hw/xscom.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/xscom.c b/hw/xscom.c
> index 0eda567fc..500b6c0e9 100644
> --- a/hw/xscom.c
> +++ b/hw/xscom.c
> @@ -72,10 +72,13 @@ static inline void *xscom_addr(uint32_t gcid, uint32_t pcb_addr)
>  static uint64_t xscom_wait_done(void)
>  {
>  	uint64_t hmer;
> +	int retry_cnt = 0;
>  
> -	do
> +	do {
>  		hmer = mfspr(SPR_HMER);
> -	while(!(hmer & SPR_HMER_XSCOM_DONE));
> +		if (retry_cnt++ > 5)
> +			break;

AFAIKS you'd better return SPR_HMER_XSCOM_FAIL here.

Thanks,
Nick

> +	} while(!(hmer & SPR_HMER_XSCOM_DONE));
>  
>  	/*
>  	 * HW822317: We need to read a second time as the actual