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From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: andrew.murray@arm.com, mathieu.poirier@linaro.org,
	alexander.shishkin@linux.intel.com
Cc: Al.Grant@arm.com, coresight@lists.linaro.org, leo.yan@linaro.org,
	Sudeep.Holla@arm.com, linux-arm-kernel@lists.infradead.org,
	mike.leach@linaro.org
Subject: Re: [PATCH v4 5/6] coresight: etm4x: save/restore state across CPU low power states
Date: Fri, 2 Aug 2019 11:54:12 +0100
Message-ID: <3bbc2a3c-03e3-7c8d-8f44-939f172bd1a0@arm.com> (raw)
In-Reply-To: <20190730125157.884-6-andrew.murray@arm.com>



On 30/07/2019 13:51, Andrew Murray wrote:
> Some hardware will ignore bit TRCPDCR.PU which is used to signal
> to hardware that power should not be removed from the trace unit.
> Let's mitigate against this by conditionally saving and restoring
> the trace unit state when the CPU enters low power states.
> 
> This patchset introduces a firmware property named
> 'arm,coresight-needs-save-restore' - when this is present the
> hardware state will be conditionally saved and restored.
> 
> A module parameter 'pm_save_enable' is also introduced which can
> be configured to override the firmware property. This can be set
> to never allow save/restore, to conditionally allow it, or to
> do as the firmware indicates (default).
> 
> We avoid saving the hardware state when coresight isn't in use
> to reduce PM latency - we can't determine this by reading the
> claim tags (TRCCLAIMCLR) as these are 'trace' registers which need
> power and clocking, something we can't easily provide in the PM
> context. Therefore we rely on the existing drvdata->mode internal
> state that is set when self-hosted coresight is used (and powered).
> 
> As we do not have a simple way of determining if an external agent
> is using coresight, we don't save/restore for this use case.
> 
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-etm4x.c | 322 ++++++++++++++++++
>   drivers/hwtracing/coresight/coresight-etm4x.h |  64 ++++
>   2 files changed, 386 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> index a128b5063f46..30f118792289 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c


> +static int etm4_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
> +			      void *v)
> +{
> +	struct etmv4_drvdata *drvdata;
> +	unsigned int cpu = smp_processor_id();
> +
> +	if (!etmdrvdata[cpu])
> +		return 0;
> +
> +	drvdata = etmdrvdata[cpu];
> +
> +	if (!drvdata->save_state)
> +		return NOTIFY_OK;
> +
> +	if (WARN_ON_ONCE(drvdata->cpu != smp_processor_id()))
> +		return NOTIFY_BAD;

minor nit: you may skip the second call to smp_processor_id() as this is called
on from non-preemptible context.

> +
> +	switch (cmd) {
> +	case CPU_PM_ENTER:
> +		/* save the state if self-hosted coresight is in use */
> +		if (local_read(&drvdata->mode))
> +			if (etm4_cpu_save(drvdata))
> +				return NOTIFY_BAD;
> +		break;
> +	case CPU_PM_EXIT:
> +	case CPU_PM_ENTER_FAILED:
> +		/* trcclaimset is set when there is state to restore */
> +		if (drvdata->state_needs_restore)
> +			etm4_cpu_restore(drvdata);
> +		break;
> +	default:
> +		return NOTIFY_DONE;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +


> +static void etm4_cpu_pm_unregister(void)
> +{
> +	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
> +}
> +#else
> +static int etm4_cpu_pm_register(void) { return 0; }
> +static void etm4_cpu_pm_unregister(void) { }
> +#endif
> +
> +static inline bool etm4_needs_save_restore(struct device *dev)
> +{
> +	return fwnode_property_present(dev->fwnode,

nit: It may be safe to use dev_fwnode(dev), instead of dev->fwnode. But I
see a lot of existing users of dev->fwnode. Not sure it does have an impact.

Looks fine to me ,

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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  parent reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 12:51 [PATCH v4 0/6] coresight: etm4x: save/restore ETMv4 context " Andrew Murray
2019-07-30 12:51 ` [PATCH v4 1/6] coresight: etm4x: remove superfluous setting of os_unlock Andrew Murray
2019-07-30 12:51 ` [PATCH v4 2/6] coresight: etm4x: use explicit barriers on enable/disable Andrew Murray
2019-08-01 13:31   ` Sasha Levin
2019-08-01 14:48     ` Mathieu Poirier
2019-08-02 18:08   ` Sasha Levin
2019-07-30 12:51 ` [PATCH v4 3/6] coresight: etm4x: use module_param instead of module_param_named Andrew Murray
2019-08-02 10:23   ` Suzuki K Poulose
2019-07-30 12:51 ` [PATCH v4 4/6] coresight: etm4x: improve clarity of etm4_os_unlock comment Andrew Murray
2019-07-30 12:51 ` [PATCH v4 5/6] coresight: etm4x: save/restore state across CPU low power states Andrew Murray
2019-07-30 21:16   ` Mathieu Poirier
2019-07-30 21:45     ` Andrew Murray
2019-07-31  8:16       ` Mike Leach
2019-07-31  9:45         ` Andrew Murray
2019-08-02 10:54   ` Suzuki K Poulose [this message]
2019-08-14  9:12     ` Andrew Murray
2019-07-30 12:51 ` [PATCH v4 6/6] dt-bindings: arm: coresight: Add support for coresight-needs-save-restore Andrew Murray
2019-08-02 10:40   ` Suzuki K Poulose
2019-08-02 14:37     ` Andrew Murray
2019-08-04 13:13       ` Mathieu Poirier
2019-08-14 10:01         ` Andrew Murray
2019-08-14 11:06           ` Mike Leach
2019-08-14 12:35             ` Suzuki K Poulose
2019-08-14 12:49               ` Andrew Murray
2019-08-14 14:20               ` Mike Leach
2019-07-30 20:12 ` [PATCH v4 0/6] coresight: etm4x: save/restore ETMv4 context across CPU low power states Mathieu Poirier
2019-07-30 21:46   ` Andrew Murray

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