Re: [PATCH v2 2/2] coresight: cti: Add CPU idle pm notifer to CTI devices.

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Mon, May 04, 2020 at 05:15:30PM +0100, Mike Leach wrote:
> Adds a notify callback for CPU PM events to the CTI driver - for
> CPU bound CTI devices.
> 
> Signed-off-by: Mike Leach <mike.leach@linaro.org>
> ---
>  drivers/hwtracing/coresight/coresight-cti.c | 82 +++++++++++++++++++++
>  1 file changed, 82 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-cti.c b/drivers/hwtracing/coresight/coresight-cti.c
> index 9af66719ae5b..0f0c14528701 100644
> --- a/drivers/hwtracing/coresight/coresight-cti.c
> +++ b/drivers/hwtracing/coresight/coresight-cti.c
> @@ -8,6 +8,7 @@
>  #include <linux/atomic.h>
>  #include <linux/bits.h>
>  #include <linux/coresight.h>
> +#include <linux/cpu_pm.h>
>  #include <linux/device.h>
>  #include <linux/io.h>
>  #include <linux/kernel.h>
> @@ -655,6 +656,84 @@ static void cti_remove_conn_xrefs(struct cti_drvdata *drvdata)
>  	}
>  }
>  
> +/** cti PM callbacks **/
> +static int cti_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
> +			     void *v)
> +{
> +	struct cti_drvdata *drvdata;
> +	unsigned int cpu = smp_processor_id();
> +	int notify_res = NOTIFY_OK;
> +
> +	if (!cti_cpu_drvdata[cpu])
> +		return NOTIFY_OK;
> +
> +	drvdata = cti_cpu_drvdata[cpu];
> +
> +	if (WARN_ON_ONCE(drvdata->ctidev.cpu != cpu))
> +		return NOTIFY_BAD;
> +
> +	spin_lock(&drvdata->spinlock);
> +
> +	switch (cmd) {
> +	case CPU_PM_ENTER:
> +		/* CTI regs all static - we have a copy & nothing to save */
> +		drvdata->config.hw_powered = false;
> +		if (drvdata->config.hw_enabled)
> +			coresight_disclaim_device(drvdata->base);
> +		break;
> +
> +	case CPU_PM_ENTER_FAILED:
> +		drvdata->config.hw_powered = true;
> +		if (drvdata->config.hw_enabled) {
> +			if (coresight_claim_device(drvdata->base))
> +				drvdata->config.hw_enabled = false;
> +		}
> +		break;
> +
> +	case CPU_PM_EXIT:
> +		/* write hardware registers to re-enable. */
> +		drvdata->config.hw_powered = true;
> +		drvdata->config.hw_enabled = false;
> +
> +		/* check enable reference count to enable HW */
> +		if (atomic_read(&drvdata->config.enable_req_count)) {
> +			/* check we can claim the device as we re-power */
> +			if (coresight_claim_device(drvdata->base))
> +				goto cti_notify_exit;
> +
> +			drvdata->config.hw_enabled = true;
> +			cti_write_all_hw_regs(drvdata);
> +		}
> +		break;
> +
> +	default:
> +		notify_res = NOTIFY_DONE;
> +		break;
> +	}
> +
> +cti_notify_exit:
> +	spin_unlock(&drvdata->spinlock);
> +	return notify_res;
> +}
> +
> +static struct notifier_block cti_cpu_pm_nb = {
> +	.notifier_call = cti_cpu_pm_notify,
> +};
> +
> +static int cti_cpu_pm_register(void)
> +{
> +	if (IS_ENABLED(CONFIG_CPU_PM))
> +		return cpu_pm_register_notifier(&cti_cpu_pm_nb);

Looking further into function cpu_pm_register_notifier(), it simply returns '0'
if CONFIG_CPU_PM is not defined.  As such cpu_pm_register_notifier() can be
called directly from cti_probe().  The same applies to
cpu_pm_unregister_notifier().

> +
> +	return 0;
> +}
> +
> +static void cti_cpu_pm_unregister(void)
> +{
> +	if (IS_ENABLED(CONFIG_CPU_PM))
> +		cpu_pm_unregister_notifier(&cti_cpu_pm_nb);
> +}
> +
>  /* CPU HP handlers */
>  static int cti_starting_cpu(unsigned int cpu)
>  {
> @@ -686,6 +765,8 @@ static void cti_pm_release(struct cti_drvdata *drvdata)
>  {
>  	if (drvdata->ctidev.cpu >= 0) {
>  		if (--nr_cti_cpu == 0) {
> +			cti_cpu_pm_unregister();
> +
>  			cpuhp_remove_state_nocalls(
>  				CPUHP_AP_ARM_CORESIGHT_CTI_STARTING);
>  		}
> @@ -814,6 +895,7 @@ static int cti_probe(struct amba_device *adev, const struct amba_id *id)
>  				"arm/coresight_cti:starting",
>  				cti_starting_cpu, cti_dying_cpu);
>  
> +			ret = cti_cpu_pm_register();

This should be one only if cpuhp_remove_state_nocalls() hasn't returned an
error.

Otherwise this looks good.

Thanks,
Mathieu

>  			cpus_read_unlock();
>  			if (ret)
>  				goto err_out;
> -- 
> 2.17.1
> 

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