Re: [PATCH v4 2/9] coresight: etm4x: exclude ss_status from drvdata->config

[Yeoreum Yun <yeoreum.yun@arm.com>]

Hi Leo,

> On Mon, Apr 13, 2026 at 03:19:55PM +0100, 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.
> > This includes remove TRCSSCRn from configurable item and
> > remove saving in etm4_disable_hw().
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> >  .../hwtracing/coresight/coresight-etm4x-cfg.c  |  1 -
> >  .../hwtracing/coresight/coresight-etm4x-core.c | 18 +++++-------------
> >  .../coresight/coresight-etm4x-sysfs.c          |  7 ++-----
> >  drivers/hwtracing/coresight/coresight-etm4x.h  |  4 +++-
> >  4 files changed, 10 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 6443f3717b37..8ebfd3924143 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 &&
> > -	       (drvdata->config.ss_status[n] & TRCSSCSRn_PC);
> > +	       (caps->ss_status[n] & TRCSSCSRn_PC);
>
> Nitpick: The naming 'ss_status' is a bit confused for capability.
> Could we rename 'ss_status' to 'ss_comparator' or a simple one
> 'ss_cmp' ?

Okay.

>
> >  }
> >
> >  u64 etm4x_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
> > @@ -571,11 +571,9 @@ 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, caps->ss_status[i], TRCSSCSRn(i));
>
> It is a bit weird to use caps to write a register.  A smooth way is to
> clear STATUS and PENDING bits based on the read back value:
>
>   val = etm4x_relaxed_read32(csa, TRCSSCSRn(i));
>   val &= ~(TRCSSCSRn_STATUS | TRCSSCSRn_PENDING);
>   etm4x_relaxed_write32(csa, val, TRCSSCSRn(i));

TBH, this is what I want to avoid. anyway Why do we need to
read again TRCSSCSR<n>? I think it's enough to write caps->ss_cmp
for clear purpose or
since the cap->ss_cmp will be all RO fields, It seems to better
to write "0" in here without reading TRCSSSR again.
>
> >  		if (etm4x_sspcicrn_present(drvdata, i))
> >  			etm4x_relaxed_write32(csa, config->ss_pe_cmp[i], TRCSSPCICRn(i));
> >  	}
> > @@ -1053,12 +1051,6 @@ 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] =
> > @@ -1501,8 +1493,8 @@ 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_status[i] = etm4x_relaxed_read32(csa, TRCSSCSRn(i));
> > +		caps->ss_status[i] &= ~(TRCSSCSRn_STATUS | TRCSSCSRn_PENDING);
>
> For init cap, we can use explict way:
>
>   caps->ss_cmp &= (TRCSSCSRn_PC | TRCSSCSRn_DV |
>                    TRCSSCSRn_DA | TRCSSCSRn_INST);

Okay.

>
> >  	}
> >  	/* NUMCIDC, bits[27:24] number of Context ID comparators for tracing */
> >  	caps->numcidc = FIELD_GET(TRCIDR4_NUMCIDC_MASK, etmidr4);
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > index 50408215d1ac..dd62f01674cf 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > @@ -1827,8 +1827,6 @@ static ssize_t sshot_ctrl_store(struct device *dev,
> >  	raw_spin_lock(&drvdata->spinlock);
> >  	idx = config->ss_idx;
> >  	config->ss_ctrl[idx] = FIELD_PREP(TRCSSCCRn_SAC_ARC_RST_MASK, val);
> > -	/* must clear bit 31 in related status register on programming */
> > -	config->ss_status[idx] &= ~TRCSSCSRn_STATUS;
> >  	raw_spin_unlock(&drvdata->spinlock);
> >  	return size;
> >  }
> > @@ -1839,10 +1837,11 @@ static ssize_t sshot_status_show(struct device *dev,
> >  {
> >  	unsigned long val;
> >  	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > +	const struct etmv4_caps *caps = &drvdata->caps;
> >  	struct etmv4_config *config = &drvdata->config;
> >
> >  	raw_spin_lock(&drvdata->spinlock);
> > -	val = config->ss_status[config->ss_idx];
> > +	val = caps->ss_status[config->ss_idx];
>
> I think cap->ss_cmp is a good refactoring, but for legacy reason, I am
> just wandering if we still need config->ss_status so that it can record
> the lastest status (mainly for STATUS bit and PENDING bit).
>
> Otherwise, this Sysfs interface can only provide capability rather
> than status value.

The legacy *totally* isn't understandable.
Since config->ss_status is *updated* at "disable" -- end of sysfs session,
STATUS and PENDING bit doesn't have any meaning in here
and while running a session config->ss_status isn't updated all
So, I don't believe there was any user who care about this bit via
sysfs interface.

Therefore, I think we can refactor with caps->ss_cmp. let's drop the
useless and meaningless information.

>
> Thanks,
> Leo
>
> >  	raw_spin_unlock(&drvdata->spinlock);
> >  	return scnprintf(buf, PAGE_SIZE, "%#lx\n", val);
> >  }
> > @@ -1877,8 +1876,6 @@ static ssize_t sshot_pe_ctrl_store(struct device *dev,
> >  	raw_spin_lock(&drvdata->spinlock);
> >  	idx = config->ss_idx;
> >  	config->ss_pe_cmp[idx] = FIELD_PREP(TRCSSPCICRn_PC_MASK, val);
> > -	/* must clear bit 31 in related status register on programming */
> > -	config->ss_status[idx] &= ~TRCSSCSRn_STATUS;
> >  	raw_spin_unlock(&drvdata->spinlock);
> >  	return size;
> >  }
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> > index 8168676f2945..8864cfb76bad 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> > @@ -213,6 +213,7 @@
> >  #define TRCACATRn_EXLEVEL_MASK			GENMASK(14, 8)
> >
> >  #define TRCSSCSRn_STATUS			BIT(31)
> > +#define TRCSSCSRn_PENDING			BIT(30)
> >  #define TRCSSCCRn_SAC_ARC_RST_MASK		GENMASK(24, 0)
> >
> >  #define TRCSSPCICRn_PC_MASK			GENMASK(7, 0)
> > @@ -861,6 +862,7 @@ enum etm_impdef_type {
> >   * @lpoverride:	If the implementation can support low-power state over.
> >   * @skip_power_up: Indicates if an implementation can skip powering up
> >   *		   the trace unit.
> > + * @ss_status:	The status of the corresponding single-shot comparator.
> >   */
> >  struct etmv4_caps {
> >  	u8	nr_pe;
> > @@ -899,6 +901,7 @@ struct etmv4_caps {
> >  	bool	atbtrig : 1;
> >  	bool	lpoverride : 1;
> >  	bool	skip_power_up : 1;
> > +	u32	ss_status[ETM_MAX_SS_CMP];
> >  };
> >
> >  /**
> > @@ -977,7 +980,6 @@ struct etmv4_config {
> >  	u32				res_ctrl[ETM_MAX_RES_SEL]; /* TRCRSCTLRn */
> >  	u8				ss_idx;
> >  	u32				ss_ctrl[ETM_MAX_SS_CMP];
> > -	u32				ss_status[ETM_MAX_SS_CMP];
> >  	u32				ss_pe_cmp[ETM_MAX_SS_CMP];
> >  	u8				addr_idx;
> >  	u64				addr_val[ETM_MAX_SINGLE_ADDR_CMP];
> > --
> > LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
> >

--
Sincerely,
Yeoreum Yun