Subject: Re: [PATCH v5 1/3] coresight: etm4x: save/restore state across CPU low power states

From: Mathieu Poirier <[email-masked]>
Date: Tue, 20 Aug 2019 15:55:37 -0600

Hi Andrew,

On Fri, Aug 16, 2019 at 04:46:13PM +0100, 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-loses-context-with-cpu' - 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 or to conditionally allow it (only for
> self-hosted). The default value is determined by firmware.
> 
> We avoid saving the hardware state when self-hosted 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).
> 
> Signed-off-by: Andrew Murray <[email-masked]>
> ---
>  drivers/hwtracing/coresight/coresight-etm4x.c | 318 ++++++++++++++++++
>  drivers/hwtracing/coresight/coresight-etm4x.h |  64 ++++
>  drivers/hwtracing/coresight/coresight.c       |   6 +
>  include/linux/coresight.h                     |   6 +
>  4 files changed, 394 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> index a128b5063f46..35a524eec36d 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> @@ -18,6 +18,7 @@
>  #include <linux/stat.h>
>  #include <linux/clk.h>
>  #include <linux/cpu.h>
> +#include <linux/cpu_pm.h>
>  #include <linux/coresight.h>
>  #include <linux/coresight-pmu.h>
>  #include <linux/pm_wakeup.h>
> @@ -26,6 +27,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/perf_event.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/property.h>
>  #include <asm/sections.h>
>  #include <asm/local.h>
>  #include <asm/virt.h>
> @@ -37,6 +39,15 @@ static int boot_enable;
>  module_param(boot_enable, int, 0444);
>  MODULE_PARM_DESC(boot_enable, "Enable tracing on boot");
>  
> +#define PARAM_PM_SAVE_FIRMWARE	  0 /* save self-hosted state as per firmware */
> +#define PARAM_PM_SAVE_NEVER	  1 /* never save any state */
> +#define PARAM_PM_SAVE_SELF_HOSTED 2 /* save self-hosted state only */
> +
> +static int pm_save_enable = PARAM_PM_SAVE_FIRMWARE;
> +module_param(pm_save_enable, int, 0444);
> +MODULE_PARM_DESC(pm_save_enable,
> +	"Save/restore state on power down: 1 = never, 2 = self-hosted");
> +
>  /* The number of ETMv4 currently registered */
>  static int etm4_count;
>  static struct etmv4_drvdata *etmdrvdata[NR_CPUS];
> @@ -54,6 +65,14 @@ static void etm4_os_unlock(struct etmv4_drvdata *drvdata)
>  	isb();
>  }
>  
> +static void etm4_os_lock(struct etmv4_drvdata *drvdata)
> +{
> +	/* Writing 0x1 to TRCOSLAR locks the trace registers */
> +	writel_relaxed(0x1, drvdata->base + TRCOSLAR);
> +	drvdata->os_unlock = false;
> +	isb();
> +}
> +
>  static bool etm4_arch_supported(u8 arch)
>  {
>  	/* Mask out the minor version number */
> @@ -1085,6 +1104,288 @@ static void etm4_init_trace_id(struct etmv4_drvdata *drvdata)
>  	drvdata->trcid = coresight_get_trace_id(drvdata->cpu);
>  }
>  
> +#ifdef CONFIG_CPU_PM
> +static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
> +{
> +	int i, ret = 0;
> +	struct etmv4_save_state *state;
> +	struct device *etm_dev = &drvdata->csdev->dev;
> +
> +	/*
> +	 * As recommended by 3.4.1 ("The procedure when powering down the PE")
> +	 * of ARM IHI 0064D
> +	 */
> +	dsb(sy);
> +	isb();
> +
> +	CS_UNLOCK(drvdata->base);
> +
> +	/* Lock the OS lock to disable trace and external debugger access */
> +	etm4_os_lock(drvdata);
> +
> +	/* wait for TRCSTATR.PMSTABLE to go up */
> +	if (coresight_timeout(drvdata->base, TRCSTATR,
> +					TRCSTATR_PMSTABLE_BIT, 1)) {

Indentation problems

> +		dev_err(etm_dev,
> +			"timeout while waiting for PM Stable Status\n");
> +		etm4_os_unlock(drvdata);
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	state = drvdata->save_state;
> +
> +	state->trcprgctlr = readl(drvdata->base + TRCPRGCTLR);
> +	state->trcprocselr = readl(drvdata->base + TRCPROCSELR);
> +	state->trcconfigr = readl(drvdata->base + TRCCONFIGR);
> +	state->trcauxctlr = readl(drvdata->base + TRCAUXCTLR);
> +	state->trceventctl0r = readl(drvdata->base + TRCEVENTCTL0R);
> +	state->trceventctl1r = readl(drvdata->base + TRCEVENTCTL1R);
> +	state->trcstallctlr = readl(drvdata->base + TRCSTALLCTLR);
> +	state->trctsctlr = readl(drvdata->base + TRCTSCTLR);
> +	state->trcsyncpr = readl(drvdata->base + TRCSYNCPR);
> +	state->trcccctlr = readl(drvdata->base + TRCCCCTLR);
> +	state->trcbbctlr = readl(drvdata->base + TRCBBCTLR);
> +	state->trctraceidr = readl(drvdata->base + TRCTRACEIDR);
> +	state->trcqctlr = readl(drvdata->base + TRCQCTLR);
> +
> +	state->trcvictlr = readl(drvdata->base + TRCVICTLR);
> +	state->trcviiectlr = readl(drvdata->base + TRCVIIECTLR);
> +	state->trcvissctlr = readl(drvdata->base + TRCVISSCTLR);
> +	state->trcvipcssctlr = readl(drvdata->base + TRCVIPCSSCTLR);
> +	state->trcvdctlr = readl(drvdata->base + TRCVDCTLR);
> +	state->trcvdsacctlr = readl(drvdata->base + TRCVDSACCTLR);
> +	state->trcvdarcctlr = readl(drvdata->base + TRCVDARCCTLR);
> +
> +	for (i = 0; i < drvdata->nrseqstate; i++)
> +		state->trcseqevr[i] = readl(drvdata->base + TRCSEQEVRn(i));
> +
> +	state->trcseqrstevr = readl(drvdata->base + TRCSEQRSTEVR);
> +	state->trcseqstr = readl(drvdata->base + TRCSEQSTR);
> +	state->trcextinselr = readl(drvdata->base + TRCEXTINSELR);
> +
> +	for (i = 0; i < drvdata->nr_cntr; i++) {
> +		state->trccntrldvr[i] = readl(drvdata->base + TRCCNTRLDVRn(i));
> +		state->trccntctlr[i] = readl(drvdata->base + TRCCNTCTLRn(i));
> +		state->trccntvr[i] = readl(drvdata->base + TRCCNTVRn(i));
> +	}
> +
> +	for (i = 0; i < drvdata->nr_resource * 2; i++)
> +		state->trcrsctlr[i] = readl(drvdata->base + TRCRSCTLRn(i));
> +
> +	for (i = 0; i < drvdata->nr_ss_cmp; i++) {
> +		state->trcssccr[i] = readl(drvdata->base + TRCSSCCRn(i));
> +		state->trcsscsr[i] = readl(drvdata->base + TRCSSCSRn(i));
> +		state->trcsspcicr[i] = readl(drvdata->base + TRCSSPCICRn(i));
> +	}
> +
> +	for (i = 0; i < drvdata->nr_addr_cmp * 2; i++) {
> +		state->trcacvr[i] = readl(drvdata->base + TRCACVRn(i));
> +		state->trcacatr[i] = readl(drvdata->base + TRCACATRn(i));
> +	}
> +
> +	/*
> +	 * Data trace stream is architecturally prohibited for A profile cores
> +	 * so we don't save (or later restore) trcdvcvr and trcdvcmr - As per
> +	 * section 1.3.4 ("Possible functional configurations of an ETMv4 trace
> +	 * unit") of ARM IHI 0064D.
> +	 */
> +
> +	for (i = 0; i < drvdata->numcidc; i++)
> +		state->trccidcvr[i] = readl(drvdata->base + TRCCIDCVRn(i));
> +
> +	for (i = 0; i < drvdata->numvmidc; i++)
> +		state->trcvmidcvr[i] = readl(drvdata->base + TRCVMIDCVRn(i));
> +
> +	state->trccidcctlr0 = readl(drvdata->base + TRCCIDCCTLR0);
> +	state->trccidcctlr1 = readl(drvdata->base + TRCCIDCCTLR1);
> +
> +	state->trcvmidcctlr0 = readl(drvdata->base + TRCVMIDCCTLR0);
> +	state->trcvmidcctlr0 = readl(drvdata->base + TRCVMIDCCTLR1);
> +
> +	state->trcclaimset = readl(drvdata->base + TRCCLAIMCLR);
> +
> +	state->trcpdcr = readl(drvdata->base + TRCPDCR);
> +
> +	/* wait for TRCSTATR.IDLE to go up */
> +	if (coresight_timeout(drvdata->base, TRCSTATR, TRCSTATR_IDLE_BIT, 1)) {
> +		dev_err(etm_dev,
> +			"timeout while waiting for Idle Trace Status\n");
> +		etm4_os_unlock(drvdata);
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	drvdata->state_needs_restore = true;
> +
> +	/*
> +	 * Power can be removed from the trace unit now. We do this to
> +	 * potentially save power on systems that respect the TRCPDCR_PU
> +	 * despite requesting software to save/restore state.
> +	 */
> +	writel_relaxed((state->trcpdcr & ~TRCPDCR_PU),
> +			drvdata->base + TRCPDCR);
> +
> +out:
> +	CS_LOCK(drvdata->base);
> +	return ret;
> +}
> +
> +static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
> +{
> +	int i;
> +	struct etmv4_save_state *state = drvdata->save_state;
> +
> +	CS_UNLOCK(drvdata->base);
> +
> +	writel_relaxed(state->trcclaimset, drvdata->base + TRCCLAIMSET);
> +
> +	writel_relaxed(state->trcprgctlr, drvdata->base + TRCPRGCTLR);
> +	writel_relaxed(state->trcprocselr, drvdata->base + TRCPROCSELR);
> +	writel_relaxed(state->trcconfigr, drvdata->base + TRCCONFIGR);
> +	writel_relaxed(state->trcauxctlr, drvdata->base + TRCAUXCTLR);
> +	writel_relaxed(state->trceventctl0r, drvdata->base + TRCEVENTCTL0R);
> +	writel_relaxed(state->trceventctl1r, drvdata->base + TRCEVENTCTL1R);
> +	writel_relaxed(state->trcstallctlr, drvdata->base + TRCSTALLCTLR);
> +	writel_relaxed(state->trctsctlr, drvdata->base + TRCTSCTLR);
> +	writel_relaxed(state->trcsyncpr, drvdata->base + TRCSYNCPR);
> +	writel_relaxed(state->trcccctlr, drvdata->base + TRCCCCTLR);
> +	writel_relaxed(state->trcbbctlr, drvdata->base + TRCBBCTLR);
> +	writel_relaxed(state->trctraceidr, drvdata->base + TRCTRACEIDR);
> +	writel_relaxed(state->trcqctlr, drvdata->base + TRCQCTLR);
> +
> +	writel_relaxed(state->trcvictlr, drvdata->base + TRCVICTLR);
> +	writel_relaxed(state->trcviiectlr, drvdata->base + TRCVIIECTLR);
> +	writel_relaxed(state->trcvissctlr, drvdata->base + TRCVISSCTLR);
> +	writel_relaxed(state->trcvipcssctlr, drvdata->base + TRCVIPCSSCTLR);
> +	writel_relaxed(state->trcvdctlr, drvdata->base + TRCVDCTLR);
> +	writel_relaxed(state->trcvdsacctlr, drvdata->base + TRCVDSACCTLR);
> +	writel_relaxed(state->trcvdarcctlr, drvdata->base + TRCVDARCCTLR);
> +
> +	for (i = 0; i < drvdata->nrseqstate; i++)
> +		writel_relaxed(state->trcseqevr[i],
> +					drvdata->base + TRCSEQEVRn(i));
> +
> +	writel_relaxed(state->trcseqrstevr, drvdata->base + TRCSEQRSTEVR);
> +	writel_relaxed(state->trcseqstr, drvdata->base + TRCSEQSTR);
> +	writel_relaxed(state->trcextinselr, drvdata->base + TRCEXTINSELR);
> +
> +	for (i = 0; i < drvdata->nr_cntr; i++) {
> +		writel_relaxed(state->trccntrldvr[i],
> +					drvdata->base + TRCCNTRLDVRn(i));
> +		writel_relaxed(state->trccntctlr[i],
> +					drvdata->base + TRCCNTCTLRn(i));
> +		writel_relaxed(state->trccntvr[i],
> +					drvdata->base + TRCCNTVRn(i));
> +	}
> +
> +	for (i = 0; i < drvdata->nr_resource * 2; i++)
> +		writel_relaxed(state->trcrsctlr[i],
> +					drvdata->base + TRCRSCTLRn(i));
> +
> +	for (i = 0; i < drvdata->nr_ss_cmp; i++) {
> +		writel_relaxed(state->trcssccr[i],
> +					drvdata->base + TRCSSCCRn(i));
> +		writel_relaxed(state->trcsscsr[i],
> +					drvdata->base + TRCSSCSRn(i));
> +		writel_relaxed(state->trcsspcicr[i],
> +					drvdata->base + TRCSSPCICRn(i));
> +	}
> +
> +	for (i = 0; i < drvdata->nr_addr_cmp * 2; i++) {
> +		writel_relaxed(state->trcacvr[i],
> +					drvdata->base + TRCACVRn(i));
> +		writel_relaxed(state->trcacatr[i],
> +					drvdata->base + TRCACATRn(i));
> +	}
> +
> +	for (i = 0; i < drvdata->numcidc; i++)
> +		writel_relaxed(state->trccidcvr[i],
> +					drvdata->base + TRCCIDCVRn(i));
> +
> +	for (i = 0; i < drvdata->numvmidc; i++)
> +		writel_relaxed(state->trcvmidcvr[i],
> +					drvdata->base + TRCVMIDCVRn(i));
> +
> +	writel_relaxed(state->trccidcctlr0, drvdata->base + TRCCIDCCTLR0);
> +	writel_relaxed(state->trccidcctlr1, drvdata->base + TRCCIDCCTLR1);
> +
> +	writel_relaxed(state->trcvmidcctlr0, drvdata->base + TRCVMIDCCTLR0);
> +	writel_relaxed(state->trcvmidcctlr0, drvdata->base + TRCVMIDCCTLR1);
> +
> +	writel_relaxed(state->trcclaimset, drvdata->base + TRCCLAIMSET);
> +
> +	writel_relaxed(state->trcpdcr, drvdata->base + TRCPDCR);
> +
> +	drvdata->state_needs_restore = false;
> +
> +	/*
> +	 * As recommended by section 4.3.7 ("Synchronization when using the
> +	 * memory-mapped interface") of ARM IHI 0064D
> +	 */
> +	dsb(sy);
> +	isb();
> +
> +	/* Unlock the OS lock to re-enable trace and external debug access */
> +	etm4_os_unlock(drvdata);
> +	CS_LOCK(drvdata->base);
> +}
> +
> +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 != cpu))
> +		return NOTIFY_BAD;
> +
> +	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:

Implicit fallthroughs are coming to an end.  Please add a 
        /* fallthrough */ 

> +	case CPU_PM_ENTER_FAILED:
> +		/* trcclaimset is set when there is state to restore */

As far as I can tell the above comment doesn't apply anymore.

> +		if (drvdata->state_needs_restore)
> +			etm4_cpu_restore(drvdata);
> +		break;
> +	default:
> +		return NOTIFY_DONE;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block etm4_cpu_pm_nb = {
> +	.notifier_call = etm4_cpu_pm_notify,
> +};
> +
> +static int etm4_cpu_pm_register(void)
> +{
> +	return cpu_pm_register_notifier(&etm4_cpu_pm_nb);
> +}
> +
> +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 int etm4_probe(struct amba_device *adev, const struct amba_id *id)
>  {
>  	int ret;
> @@ -1101,6 +1402,17 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
>  
>  	dev_set_drvdata(dev, drvdata);
>  
> +	if (pm_save_enable == PARAM_PM_SAVE_FIRMWARE)
> +		pm_save_enable = coresight_loses_context_with_cpu(dev) ?
> +			       PARAM_PM_SAVE_SELF_HOSTED : PARAM_PM_SAVE_NEVER;
> +
> +	if (pm_save_enable != PARAM_PM_SAVE_NEVER) {
> +		drvdata->save_state = devm_kmalloc(dev,
> +				sizeof(struct etmv4_save_state), GFP_KERNEL);
> +		if (!drvdata->save_state)
> +			return -ENOMEM;
> +	}
> +
>  	/* Validity for the resource is already checked by the AMBA core */
>  	base = devm_ioremap_resource(dev, res);
>  	if (IS_ERR(base))
> @@ -1135,6 +1447,10 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
>  		if (ret < 0)
>  			goto err_arch_supported;
>  		hp_online = ret;
> +
> +		ret = etm4_cpu_pm_register();
> +		if (ret)
> +			goto err_arch_supported;
>  	}
>  
>  	cpus_read_unlock();
> @@ -1185,6 +1501,8 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
>  
>  err_arch_supported:
>  	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);
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 4523f10ddd0f..546d790cb01b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -175,6 +175,7 @@
>  					 ETM_MODE_EXCL_USER)
>  
>  #define TRCSTATR_IDLE_BIT		0
> +#define TRCSTATR_PMSTABLE_BIT		1
>  #define ETM_DEFAULT_ADDR_COMP		0
>  
>  /* PowerDown Control Register bits */
> @@ -281,6 +282,65 @@ struct etmv4_config {
>  	u32				ext_inp;
>  };
>  
> +/**
> + * struct etm4_save_state - state to be preserved when ETM is without power
> + */
> +struct etmv4_save_state {
> +	u32	trcprgctlr;
> +	u32	trcprocselr;
> +	u32	trcconfigr;
> +	u32	trcauxctlr;
> +	u32	trceventctl0r;
> +	u32	trceventctl1r;
> +	u32	trcstallctlr;
> +	u32	trctsctlr;
> +	u32	trcsyncpr;
> +	u32	trcccctlr;
> +	u32	trcbbctlr;
> +	u32	trctraceidr;
> +	u32	trcqctlr;
> +
> +	u32	trcvictlr;
> +	u32	trcviiectlr;
> +	u32	trcvissctlr;
> +	u32	trcvipcssctlr;
> +	u32	trcvdctlr;
> +	u32	trcvdsacctlr;
> +	u32	trcvdarcctlr;
> +
> +	u32	trcseqevr[ETM_MAX_SEQ_STATES];
> +	u32	trcseqrstevr;
> +	u32	trcseqstr;
> +	u32	trcextinselr;
> +	u32	trccntrldvr[ETMv4_MAX_CNTR];
> +	u32	trccntctlr[ETMv4_MAX_CNTR];
> +	u32	trccntvr[ETMv4_MAX_CNTR];
> +
> +	u32	trcrsctlr[ETM_MAX_RES_SEL * 2];
> +
> +	u32	trcssccr[ETM_MAX_SS_CMP];
> +	u32	trcsscsr[ETM_MAX_SS_CMP];
> +	u32	trcsspcicr[ETM_MAX_SS_CMP];
> +
> +	u64	trcacvr[ETM_MAX_SINGLE_ADDR_CMP];
> +	u64	trcacatr[ETM_MAX_SINGLE_ADDR_CMP];
> +	u64	trccidcvr[ETMv4_MAX_CTXID_CMP];
> +	u32	trcvmidcvr[ETM_MAX_VMID_CMP];
> +	u32	trccidcctlr0;
> +	u32	trccidcctlr1;
> +	u32	trcvmidcctlr0;
> +	u32	trcvmidcctlr1;
> +
> +	u32	trcclaimset;
> +
> +	u32	cntr_val[ETMv4_MAX_CNTR];
> +	u32	seq_state;
> +	u32	vinst_ctrl;
> +	u32	ss_status[ETM_MAX_SS_CMP];
> +
> +	u32	trcpdcr;
> +};
> +
>  /**
>   * struct etm4_drvdata - specifics associated to an ETM component
>   * @base:       Memory mapped base address for this component.
> @@ -336,6 +396,8 @@ struct etmv4_config {
>   * @atbtrig:	If the implementation can support ATB triggers
>   * @lpoverride:	If the implementation can support low-power state over.
>   * @config:	structure holding configuration parameters.
> + * @save_state:	State to be preserved across power loss
> + * @state_needs_restore: True when there is context to restore after PM exit
>   */
>  struct etmv4_drvdata {
>  	void __iomem			*base;
> @@ -381,6 +443,8 @@ struct etmv4_drvdata {
>  	bool				atbtrig;
>  	bool				lpoverride;
>  	struct etmv4_config		config;
> +	struct etmv4_save_state		*save_state;
> +	bool				state_needs_restore;
>  };
>  
>  /* Address comparator access types */
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index 6453c67a4d01..e6ca899fea4e 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -1308,6 +1308,12 @@ static inline int coresight_search_device_idx(struct coresight_dev_list *dict,
>  	return -ENOENT;
>  }
>  
> +bool coresight_loses_context_with_cpu(struct device *dev)
> +{
> +	return fwnode_property_present(dev_fwnode(dev),
> +				       "arm,coresight-loses-context-with-cpu");
> +}
> +
>  /*
>   * coresight_alloc_device_name - Get an index for a given device in the
>   * device index list specific to a driver. An index is allocated for a
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index a2b68823717b..44e552de419c 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -285,6 +285,8 @@ extern void coresight_disclaim_device(void __iomem *base);
>  extern void coresight_disclaim_device_unlocked(void __iomem *base);
>  extern char *coresight_alloc_device_name(struct coresight_dev_list *devs,
>  					 struct device *dev);
> +
> +extern bool coresight_loses_context_with_cpu(struct device *dev);
>  #else
>  static inline struct coresight_device *
>  coresight_register(struct coresight_desc *desc) { return NULL; }
> @@ -307,6 +309,10 @@ static inline int coresight_claim_device(void __iomem *base)
>  static inline void coresight_disclaim_device(void __iomem *base) {}
>  static inline void coresight_disclaim_device_unlocked(void __iomem *base) {}
>  
> +static inline bool coresight_loses_context_with_cpu(struct device *dev)
> +{
> +	return false;
> +}
>  #endif
>  
>  extern int coresight_get_cpu(struct device *dev);
> -- 
> 2.21.0
> 

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