[PATCH] ARM/ARM64: arch-timer: fix arch_timer_probed logic

[Mark Rutland]

On Wed, Oct 15, 2014 at 04:06:20PM +0100, Marc Zyngier wrote:
> Commit c387f07e6205 (clocksource: arm_arch_timer: Discard unavailable
> timers correctly) changed the way the driver makes sure both the memory
> and system-register timers have been probed before finalizing the probing.
> 
> There is a interesting flaw in this logic that leads to this final step
> never to be executed. Things seems to work pretty well until something
> actually needs the data that is produced during this final stage.
> 
> For example, KVM explodes on the first run of a guest when executed on
> a platform that has both memory and sysreg nodes (Juno, for example).

As far as I can tell, the logic is flawed for all cases except two
functional nodes that we manage to probe.

> 
> Just fix the damned logic, and enjoy booting VMs again.
> 
> Tested on a Juno system.
> 
> Cc: Sudeep Holla <sudeep.holla at arm.com>
> Cc: Stephen Boyd <sboyd at codeaurora.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Daniel Lezcano <daniel.lezcano at linaro.org>
> Cc: Christoffer Dall <christoffer.dall at linaro.org>
> Reported-by: Riku Voipio <riku.voipio at linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>

The new logic makes sense to me, so:

Acked-by: Mark Rutland <mark.rutland at arm.com>

Thanks,
Mark.

> ---
>  drivers/clocksource/arm_arch_timer.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 2133f9d..43005d4 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -660,11 +660,11 @@ static bool __init
>  arch_timer_probed(int type, const struct of_device_id *matches)
>  {
>  	struct device_node *dn;
> -	bool probed = false;
> +	bool probed = true;
>  
>  	dn = of_find_matching_node(NULL, matches);
> -	if (dn && of_device_is_available(dn) && (arch_timers_present & type))
> -		probed = true;
> +	if (dn && of_device_is_available(dn) && !(arch_timers_present & type))
> +		probed = false;
>  	of_node_put(dn);
>  
>  	return probed;
> -- 
> 2.0.4
> 
>