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Date:   Wed, 17 Mar 2021 11:09:45 -0600
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     Suzuki K Poulose <suzuki.poulose@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        mike.leach@linaro.org, anshuman.khandual@arm.com,
        leo.yan@linaro.org
Subject: Re: [PATCH v4 09/19] coresight: etm4x: Move ETM to prohibited region
 for disable
Message-ID: <20210317170945.GA1498234@xps15>
References: <20210225193543.2920532-1-suzuki.poulose@arm.com>
 <20210225193543.2920532-10-suzuki.poulose@arm.com>
 <20210316193008.GD1387186@xps15>
 <7e8569f8-9da2-096c-a35a-14248329026a@arm.com>
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In-Reply-To: <7e8569f8-9da2-096c-a35a-14248329026a@arm.com>
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On Wed, Mar 17, 2021 at 10:44:51AM +0000, Suzuki K Poulose wrote:
> Hi Mathieu
> 
> On 3/16/21 7:30 PM, Mathieu Poirier wrote:
> > On Thu, Feb 25, 2021 at 07:35:33PM +0000, Suzuki K Poulose wrote:
> > > If the CPU implements Arm v8.4 Trace filter controls (FEAT_TRF),
> > > move the ETM to trace prohibited region using TRFCR, while disabling.
> > > 
> > > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > > Cc: Mike Leach <mike.leach@linaro.org>
> > > Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > ---
> > > New patch
> > 
> > I would ask you to refrain from introducing new patches.  Otherwise the goal
> > posts keep on moving with every revision and we'll never get through.  Fixes and
> > enhancement can come in later patchsets.
> > 
> 
> While I agree that this is a fix and a new patch, it also attests what
> we do in the nvhe hypervisor to disable tracing while we enter the guest, by
> using the Trace filter controls.
> 
> > > ---
> > >   .../coresight/coresight-etm4x-core.c          | 21 +++++++++++++++++--
> > >   drivers/hwtracing/coresight/coresight-etm4x.h |  2 ++
> > >   2 files changed, 21 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > index 15016f757828..00297906669c 100644
> > > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > @@ -31,6 +31,7 @@
> > >   #include <linux/pm_runtime.h>
> > >   #include <linux/property.h>
> > > +#include <asm/barrier.h>
> > >   #include <asm/sections.h>
> > >   #include <asm/sysreg.h>
> > >   #include <asm/local.h>
> > > @@ -654,6 +655,7 @@ static int etm4_enable(struct coresight_device *csdev,
> > >   static void etm4_disable_hw(void *info)
> > >   {
> > >   	u32 control;
> > > +	u64 trfcr;
> > >   	struct etmv4_drvdata *drvdata = info;
> > >   	struct etmv4_config *config = &drvdata->config;
> > >   	struct coresight_device *csdev = drvdata->csdev;
> > > @@ -676,6 +678,16 @@ static void etm4_disable_hw(void *info)
> > >   	/* EN, bit[0] Trace unit enable bit */
> > >   	control &= ~0x1;
> > > +	/*
> > > +	 * If the CPU supports v8.4 Trace filter Control,
> > > +	 * set the ETM to trace prohibited region.
> > > +	 */
> > > +	if (drvdata->trfc) {
> > > +		trfcr = read_sysreg_s(SYS_TRFCR_EL1);
> > > +		write_sysreg_s(trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE),
> > > +			       SYS_TRFCR_EL1);
> > > +		isb();
> > > +	}
> > >   	/*
> > >   	 * Make sure everything completes before disabling, as recommended
> > >   	 * by section 7.3.77 ("TRCVICTLR, ViewInst Main Control Register,
> > > @@ -683,12 +695,16 @@ static void etm4_disable_hw(void *info)
> > >   	 */
> > >   	dsb(sy);
> > >   	isb();
> > > +	/* Trace synchronization barrier, is a nop if not supported */
> > > +	tsb_csync();
> > >   	etm4x_relaxed_write32(csa, control, TRCPRGCTLR);
> > >   	/* wait for TRCSTATR.PMSTABLE to go to '1' */
> > >   	if (coresight_timeout(csa, TRCSTATR, TRCSTATR_PMSTABLE_BIT, 1))
> > >   		dev_err(etm_dev,
> > >   			"timeout while waiting for PM stable Trace Status\n");
> > > +	if (drvdata->trfc)
> > > +		write_sysreg_s(trfcr, SYS_TRFCR_EL1);
> > 
> > drvdata->trfc is invariably set to true in cpu_enable_tracing() and as such
> > testing for it is not required.
> 
> That is not true. This is only set when the CPU supports trace filtering.
> So, this is more of a capability field for the CPU where the ETM is bound.
> Only v8.4+ CPUs implement trace filtering controls.

Ah yes, you are correct - this patch makes sense now.

> 
> Cheers
> Suzuki
> 
> 
> > 
> > >   	/* read the status of the single shot comparators */
> > >   	for (i = 0; i < drvdata->nr_ss_cmp; i++) {
> > > @@ -873,7 +889,7 @@ static bool etm4_init_csdev_access(struct etmv4_drvdata *drvdata,
> > >   	return false;
> > >   }
> > > -static void cpu_enable_tracing(void)
> > > +static void cpu_enable_tracing(struct etmv4_drvdata *drvdata)
> > >   {
> > >   	u64 dfr0 = read_sysreg(id_aa64dfr0_el1);
> > >   	u64 trfcr;
> > > @@ -881,6 +897,7 @@ static void cpu_enable_tracing(void)
> > >   	if (!cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_TRACE_FILT_SHIFT))
> > >   		return;
> > > +	drvdata->trfc = true;
> > >   	/*
> > >   	 * If the CPU supports v8.4 SelfHosted Tracing, enable
> > >   	 * tracing at the kernel EL and EL0, forcing to use the
> > > @@ -1082,7 +1099,7 @@ static void etm4_init_arch_data(void *info)
> > >   	/* NUMCNTR, bits[30:28] number of counters available for tracing */
> > >   	drvdata->nr_cntr = BMVAL(etmidr5, 28, 30);
> > >   	etm4_cs_lock(drvdata, csa);
> > > -	cpu_enable_tracing();
> > > +	cpu_enable_tracing(drvdata);
> > 
> > At least for this patch, the above three hunks aren't needed.
> > 
> > >   }
> > >   static inline u32 etm4_get_victlr_access_type(struct etmv4_config *config)
> > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> > > index 0af60571aa23..f6478ef642bf 100644
> > > --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> > > +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> > > @@ -862,6 +862,7 @@ struct etmv4_save_state {
> > >    * @nooverflow:	Indicate if overflow prevention is supported.
> > >    * @atbtrig:	If the implementation can support ATB triggers
> > >    * @lpoverride:	If the implementation can support low-power state over.
> > > + * @trfc:	If the implementation supports Arm v8.4 trace filter controls.
> > >    * @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
> > > @@ -912,6 +913,7 @@ struct etmv4_drvdata {
> > >   	bool				nooverflow;
> > >   	bool				atbtrig;
> > >   	bool				lpoverride;
> > > +	bool				trfc;
> > 
> > Nor is this one.
> > 
> > >   	struct etmv4_config		config;
> > >   	struct etmv4_save_state		*save_state;
> > >   	bool				state_needs_restore;
> > > -- 
> > > 2.24.1
> > > 
>