Subject: Re: [PATCH v5 04/12] coresight: etm4x: exclude ss_status from drvdata->config

From: Yeoreum Yun <[email-masked]>
Date: Thu, 16 Apr 2026 07:54:21 +0100

Hi Jie,

>
>
> On 4/16/2026 12:55 AM, Yeoreum Yun wrote:
> > The purpose of TRCSSCSRn register is to show status of
> > the corresponding Single-shot Comparator Control and input supports.
> > That means writable field's purpose for reset or restore from idle status
> > not for configuration.
> >
> > Therefore, exclude ss_status from drvdata->config, move it to etm4x_caps
> > and rename it to ss_smp.
> >
> > This includes remove TRCSSCRn from configurable item and
> > remove saving in etm4_disable_hw().
> >
> > Signed-off-by: Yeoreum Yun <[email-masked]>
> > ---
> >   .../hwtracing/coresight/coresight-etm4x-cfg.c |  1 -
> >   .../coresight/coresight-etm4x-core.c          | 19 ++++++-------------
> >   .../coresight/coresight-etm4x-sysfs.c         |  7 ++-----
> >   drivers/hwtracing/coresight/coresight-etm4x.h |  7 ++++++-
> >   4 files changed, 14 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> > index c302072b293a..d14d7c8a23e5 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> > @@ -86,7 +86,6 @@ static int etm4_cfg_map_reg_offset(struct etmv4_drvdata *drvdata,
> >   		off_mask =  (offset & GENMASK(11, 5));
> >   		do {
> >   			CHECKREGIDX(TRCSSCCRn(0), ss_ctrl, idx, off_mask);
> > -			CHECKREGIDX(TRCSSCSRn(0), ss_status, idx, off_mask);
> >   			CHECKREGIDX(TRCSSPCICRn(0), ss_pe_cmp, idx, off_mask);
> >   		} while (0);
> >   	} else if ((offset >= TRCCIDCVRn(0)) && (offset <= TRCVMIDCVRn(7))) {
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > index b2b092a76eb5..f55338a4989d 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -91,7 +91,7 @@ static bool etm4x_sspcicrn_present(struct etmv4_drvdata *drvdata, int n)
> >   	const struct etmv4_caps *caps = &drvdata->caps;
> >   	return (n < caps->nr_ss_cmp) && caps->nr_pe_cmp &&
> > -	       (drvdata->config.ss_status[n] & TRCSSCSRn_PC);
> > +	       (caps->ss_cmp[n] & TRCSSCSRn_PC);
> >   }
> >   u64 etm4x_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
> > @@ -573,11 +573,9 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
> >   		etm4x_relaxed_write32(csa, config->res_ctrl[i], TRCRSCTLRn(i));
> >   	for (i = 0; i < caps->nr_ss_cmp; i++) {
> > -		/* always clear status bit on restart if using single-shot */
> > -		if (config->ss_ctrl[i] || config->ss_pe_cmp[i])
> > -			config->ss_status[i] &= ~TRCSSCSRn_STATUS;
> >   		etm4x_relaxed_write32(csa, config->ss_ctrl[i], TRCSSCCRn(i));
> > -		etm4x_relaxed_write32(csa, config->ss_status[i], TRCSSCSRn(i));
> > +		/* always clear status and pending bits on restart if using single-shot */
> > +		etm4x_relaxed_write32(csa, 0x0, TRCSSCSRn(i));
> >   		if (etm4x_sspcicrn_present(drvdata, i))
> >   			etm4x_relaxed_write32(csa, config->ss_pe_cmp[i], TRCSSPCICRn(i));
> >   	}
> > @@ -1055,12 +1053,6 @@ static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
> >   	etm4_disable_trace_unit(drvdata);
> > -	/* read the status of the single shot comparators */
> > -	for (i = 0; i < caps->nr_ss_cmp; i++) {
> > -		config->ss_status[i] =
> > -			etm4x_relaxed_read32(csa, TRCSSCSRn(i));
> > -	}
> > -
> >   	/* read back the current counter values */
> >   	for (i = 0; i < caps->nr_cntr; i++) {
> >   		config->cntr_val[i] =
> > @@ -1503,8 +1495,9 @@ static void etm4_init_arch_data(void *info)
> >   	 */
> >   	caps->nr_ss_cmp = FIELD_GET(TRCIDR4_NUMSSCC_MASK, etmidr4);
> >   	for (i = 0; i < caps->nr_ss_cmp; i++) {
> > -		drvdata->config.ss_status[i] =
> > -			etm4x_relaxed_read32(csa, TRCSSCSRn(i));
> > +		caps->ss_cmp[i] = etm4x_relaxed_read32(csa, TRCSSCSRn(i));
> > +		caps->ss_cmp[i] &= (TRCSSCSRn_PC | TRCSSCSRn_DV |
> > +				    TRCSSCSRn_DA | TRCSSCSRn_INST);
>
> Just re-go through this patch and had a question here:
>
> I’m not sure whether this new change should be documented in the ABI, given
> that the TRCSSCSRn_STATUS bit is masked. In my opinion, this change breaks
> the existing ABI description.
>
> Description from the ABI document:
>
> What:           /sys/bus/coresight/devices/etm<N>/sshot_status
> Date:           December 2019
> KernelVersion:  5.5
> Contact:        Mathieu Poirier <[email-masked]>
> Description:    (Read) Print the current value of the selected single
>                 shot status register.

But, as I mentioned another thread:
  - https://lore.kernel.org/all/[email-masked]/

Till now, sysfs doesn't show the *current value* of the single shot
state since the config->ss_status is updated enabled/disabled sysfs
session. an I think once the session is disabled, other status bits
(currently STATUS and PENDING bits) don't have any meaning.

I think it's enough to change the doc's Description for this.

Any thought?

--
Sincerely,
Yeoreum Yun