[PATCH] coresight: etmv4: Fix CPU power management setup in probe() function.

[Mathieu Poirier]

Hi Mike,

On Tue, Jun 23, 2020 at 09:46:06PM +0100, Mike Leach wrote:
> The current probe() function calls a pair of cpuhp_xxx API functions to
> setup CPU hotplug handling. The hotplug lock is held for the duration of
> the two calls and other CPU related code using cpus_read_lock() /
> cpus_read_unlock() calls.
> 
> The problem is that on error states, goto: statements bypass the
> cpus_read_unlock() call. This code has increased in complexity as the
> driver has developed.
> 
> This patch introduces a pair of helper functions etm4_pm_setup() and
> etm4_pm_clear() which correct the issues above and group the PM code a
> little better.
> 
> The two functions etm4_cpu_pm_register() and etm4_cpu_pm_unregister() are
> dropped as these call cpu_pm_register_notifier() / ..unregister_notifier()
> dependent on CONFIG_CPU_PM - but this define is used to nop these functions
> out in the pm headers - so the wrapper functions are superfluous.
> 
> Fixes: f188b5e76aae ("coresight: etm4x: Save/restore state across CPU low power states")
> Fixes: e9f5d63f84fe ("hwtracing/coresight-etm4x: Use cpuhp_setup_state_nocalls_cpuslocked()")
> Fixes: 58eb457be028 ("etm4x: Convert to hotplug state machine")
> 
> Signed-off-by: Mike Leach <mike.leach at linaro.org>
> ---
>  drivers/hwtracing/coresight/coresight-etm4x.c | 79 ++++++++++++-------
>  1 file changed, 51 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> index 919b76fa49c4..4dd59de440de 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> @@ -1407,18 +1407,56 @@ static struct notifier_block etm4_cpu_pm_nb = {
>  	.notifier_call = etm4_cpu_pm_notify,
>  };
>  
> -static int etm4_cpu_pm_register(void)
> +/* Setup PM. Called with cpus locked. Deals with error conditions and counts */
> +static int etm4_pm_setup_cpuslocked(void)
>  {
> -	if (IS_ENABLED(CONFIG_CPU_PM))
> -		return cpu_pm_register_notifier(&etm4_cpu_pm_nb);
> +	int ret;
>  
> -	return 0;
> +	if (etm4_count++)
> +		return 0;
> +
> +	ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb);
> +	if (ret)
> +		goto reduce_count;
> +
> +	ret = cpuhp_setup_state_nocalls_cpuslocked(
> +		CPUHP_AP_ARM_CORESIGHT_STARTING, "arm/coresight4:starting",
> +		etm4_starting_cpu, etm4_dying_cpu);

The 80 character limit per line has been relaxed to 100 in the 5.8 cycle.  As
such you can arrange CPUHP_AP_ARM_CORESIGHT_STARTING the same way you did below
with CPUHP_AP_ONLINE_DYN without getting yelled at by checkpatch.

> +
> +	if (ret)
> +		goto unregister_notifier;
> +
> +	ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN,
> +						   "arm/coresight4:online",
> +						   etm4_online_cpu, NULL);
> +
> +	/* HP dyn state ID returned in ret on success */
> +	if (ret > 0) {
> +		hp_online = ret;
> +		return 0;
> +	}
> +
> +	/* failed dyn state - remove others */
> +	cpuhp_remove_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING);
> +
> +unregister_notifier:
> +	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
> +
> +reduce_count:
> +	--etm4_count;
> +	return ret;
>  }
>  
> -static void etm4_cpu_pm_unregister(void)
> +static void etm4_pm_clear(void)
>  {
> -	if (IS_ENABLED(CONFIG_CPU_PM))
> +	if (--etm4_count == 0) {

        if (--etm4_count != 0)
                return;

>  		cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
> +		cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
> +		if (hp_online) {
> +			cpuhp_remove_state_nocalls(hp_online);
> +			hp_online = 0;
> +		}
> +	}
>  }
>  
>  static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
> @@ -1475,24 +1513,15 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
>  				etm4_init_arch_data,  drvdata, 1))
>  		dev_err(dev, "ETM arch init failed\n");
>  
> -	if (!etm4_count++) {
> -		cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING,
> -						     "arm/coresight4:starting",
> -						     etm4_starting_cpu, etm4_dying_cpu);
> -		ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN,
> -							   "arm/coresight4:online",
> -							   etm4_online_cpu, NULL);
> -		if (ret < 0)
> -			goto err_arch_supported;
> -		hp_online = ret;
> +	ret = etm4_pm_setup_cpuslocked();
> +	cpus_read_unlock();
>  
> -		ret = etm4_cpu_pm_register();
> -		if (ret)
> -			goto err_arch_supported;
> +	/* etm4_pm_setup does its own cleanup - just exit on error here */

s/etm4_pm_setup/etm4_pm_setup_cpuslocked()

Otherwise this is a good cleanup.

Thanks,
Mathieu

> +	if (ret) {
> +		etmdrvdata[drvdata->cpu] = NULL;
> +		return ret;
>  	}
>  
> -	cpus_read_unlock();
> -
>  	if (etm4_arch_supported(drvdata->arch) == false) {
>  		ret = -EINVAL;
>  		goto err_arch_supported;
> @@ -1544,13 +1573,7 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
>  
>  err_arch_supported:
>  	etmdrvdata[drvdata->cpu] = NULL;
> -	if (--etm4_count == 0) {
> -		etm4_cpu_pm_unregister();
> -
> -		cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
> -		if (hp_online)
> -			cpuhp_remove_state_nocalls(hp_online);
> -	}
> +	etm4_pm_clear();
>  	return ret;
>  }
>  
> -- 
> 2.17.1
>