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From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, mike.leach@linaro.org,
	coresight@lists.linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 23/26] coresight: etm4x: Detect system instructions support
Date: Tue, 10 Nov 2020 10:33:03 -0700	[thread overview]
Message-ID: <20201110173303.GB3429138@xps15> (raw)
In-Reply-To: <b4a4bd73-00c5-a921-3f01-7100d2a0edf8@arm.com>

On Tue, Nov 10, 2020 at 09:31:42AM +0000, Suzuki K Poulose wrote:
> On 11/9/20 8:22 PM, Mathieu Poirier wrote:
> > On Wed, Oct 28, 2020 at 10:09:42PM +0000, Suzuki K Poulose wrote:
> > > ETM v4.4 onwards adds support for system instruction access
> > > to the ETM. Detect the support on an ETM and switch to using the
> > > mode when available.
> > > 
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > ---
> > >   .../coresight/coresight-etm4x-core.c          | 39 +++++++++++++++++++
> > >   1 file changed, 39 insertions(+)
> > > 
> > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > index 4bc2f15b6332..dc537b5612eb 100644
> > > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > @@ -675,6 +675,37 @@ static const struct coresight_ops etm4_cs_ops = {
> > >   	.source_ops	= &etm4_source_ops,
> > >   };
> > > +static inline bool cpu_supports_sysreg_trace(void)
> > > +{
> > > +	u64 dfr0 = read_sysreg_s(SYS_ID_AA64DFR0_EL1);
> > > +
> > > +	return ((dfr0 >> ID_AA64DFR0_TRACEVER_SHIFT) & 0xfUL) > 0;
> > 
> > I would do:
> > 
> >          return ((dfr0 >> ID_AA64DFR0_TRACEVER_SHIFT) & 0xfUL) == 1;
> > 
> > Because any other value than '1' are reserved.
> 
> Correct. However, this is something we follow for all ID features
> in the arm64 kernel and is clarified in the Arm ARM (ARM DDI 0487F.a) :
> 
> "D13.1.3 Principles of the ID scheme for fields in ID registers"
> 
> Which guarantees that a (field  > n) implies, everything that field == n
> is implied. (Well there are exceptions listed in the section, but
> TRACEVER is not one of those). So this should cover an old kernel
> running on a future CPU, using the features that it understands.
> (See feature_matches() in arch/arm64/kernel/cpufeature.c, which is
> the fundamental logic to detect a feature).
> 

While I haven't found anything conclusive in cpufeature.c, the documentation is
clear on the fact that versions are incremental and build on top of previous
ones.  We can proceed with the current implementation. 

> Please let me know if you're OK with the justification.
> 
> Thanks for the review.
> 
> Suzuki

  reply	other threads:[~2020-11-10 17:33 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-28 22:09 [PATCH v3 00/26] coresight: Support for ETM system instructions Suzuki K Poulose
2020-10-28 22:09 ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 01/26] coresight: etm4x: Fix accesses to TRCVMIDCTLR1 Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 02/26] coresight: etm4x: Fix accesses to TRCCIDCTLR1 Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 03/26] coresight: etm4x: Update TRCIDR3.NUMPROCS handling to match v4.2 Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 04/26] coresight: etm4x: Fix accesses to TRCPROCSELR Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 05/26] coresight: etm4x: Handle TRCVIPCSSCTLR accesses Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 06/26] coresight: etm4x: Handle access to TRCSSPCICRn Suzuki K Poulose
2020-11-02 21:46   ` Mathieu Poirier
2020-11-02 22:04     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 07/26] coresight: Introduce device access abstraction Suzuki K Poulose
2020-11-03 17:14   ` Mathieu Poirier
2020-11-03 17:25     ` Mathieu Poirier
2020-11-04 10:07       ` Suzuki K Poulose
2020-11-09 21:00   ` Mathieu Poirier
2020-11-10  9:24     ` Suzuki K Poulose
2020-11-10 17:02       ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 08/26] coresight: tpiu: Prepare for using coresight " Suzuki K Poulose
2020-11-03 18:03   ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 09/26] coresight: Convert coresight_timeout to use " Suzuki K Poulose
2020-11-03 18:03   ` Mathieu Poirier
2020-11-04 10:42     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 10/26] coresight: Convert claim/disclaim operations to use access wrappers Suzuki K Poulose
2020-11-03 18:36   ` Mathieu Poirier
2020-11-04 10:54     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 11/26] coresight: etm4x: Always read the registers on the host CPU Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 12/26] coresight: etm4x: Convert all register accesses Suzuki K Poulose
2020-11-03 18:53   ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 13/26] coresight: etm4x: Add commentary on the registers Suzuki K Poulose
2020-11-03 19:03   ` Mathieu Poirier
2020-11-03 19:04   ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 14/26] coresight: etm4x: Add sysreg access helpers Suzuki K Poulose
2020-10-29 15:26   ` Suzuki K Poulose
2020-11-05 20:52   ` Mathieu Poirier
2020-11-05 22:47     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 15/26] coresight: etm4x: Define DEVARCH register fields Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 16/26] coresight: etm4x: Check for Software Lock Suzuki K Poulose
2020-11-05 21:50   ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 17/26] coresight: etm4x: Cleanup secure exception level masks Suzuki K Poulose
2020-11-05 21:55   ` Mathieu Poirier
2020-11-09  9:40     ` Suzuki K Poulose
2020-11-09 17:42       ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 18/26] coresight: etm4x: Clean up " Suzuki K Poulose
2020-11-06 18:52   ` Mathieu Poirier
2020-11-09  9:44     ` Suzuki K Poulose
2020-11-10 23:15     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 19/26] coresight: etm4x: Detect access early on the target CPU Suzuki K Poulose
2020-11-06 20:34   ` Mathieu Poirier
2020-11-09  9:48     ` Suzuki K Poulose
2020-11-09 17:48       ` Mathieu Poirier
2020-11-06 20:46   ` Mathieu Poirier
2020-11-10 10:47     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 20/26] coresight: etm4x: Handle ETM architecture version Suzuki K Poulose
2020-11-06 21:11   ` Mathieu Poirier
2020-11-09  9:51     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 21/26] coresight: etm4x: Use TRCDEVARCH for component discovery Suzuki K Poulose
2020-11-06 21:42   ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 22/26] coresight: etm4x: Add necessary synchronization for sysreg access Suzuki K Poulose
2020-11-09 18:32   ` Mathieu Poirier
2020-11-10 10:11     ` Suzuki K Poulose
2020-11-10 11:40       ` John Horley
2020-11-10 17:35       ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 23/26] coresight: etm4x: Detect system instructions support Suzuki K Poulose
2020-11-09 20:22   ` Mathieu Poirier
2020-11-10  9:31     ` Suzuki K Poulose
2020-11-10 17:33       ` Mathieu Poirier [this message]
2020-10-28 22:09 ` [PATCH v3 24/26] coresight: etm4x: Refactor probing routine Suzuki K Poulose
2020-11-09 20:43   ` Mathieu Poirier
2020-10-28 22:09 ` [PATCH v3 25/26] coresight: etm4x: Add support for sysreg only devices Suzuki K Poulose
2020-11-09 20:46   ` Mathieu Poirier
2020-11-10 10:50     ` Suzuki K Poulose
2020-10-28 22:09 ` [PATCH v3 26/26] dts: bindings: coresight: ETM system register access only units Suzuki K Poulose
2020-11-02 15:31   ` Rob Herring
2020-11-09 20:50   ` Mathieu Poirier
2020-11-10 10:51     ` Suzuki K Poulose
2020-10-29  7:53 ` [PATCH v3 00/26] coresight: Support for ETM system instructions Mike Leach
2020-10-29 15:45   ` Suzuki K Poulose

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