Subject: Re: [PATCH v7 02/13] coresight: etm4x: fix underflow for nrseqstate

From: Yeoreum Yun <[email-masked]>
Date: Mon, 1 Jun 2026 11:15:28 +0100

> On 01/06/2026 11:08, Yeoreum Yun wrote:
> > > On 19/05/2026 16:48, Yeoreum Yun wrote:
> > > > TCRSEQEVR<n> is implemented only when TCRIDR5.NUMSEQSTATE is 0b100,
> > > > in which case n ranges from 0 to 2; otherwise, TCRIDR5.NUMSEQSTATE is 0b000.
> > > > 
> > > > Therefore, drvdata->nrseqstate should be checked before entering the loop.
> > > 
> > > for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > 
> > > Wouldn't that check cover the case ? (provided i is signed int ?)
> > > 
> > > Suzuki
> > 
> > Unfortunately, the drvdata->nrseqstate is u8 but i is signed int.
> > I think in this case it would iterate 255 times (0xff).
> 
> Then why not fix it to signed ? Anyways, please see my other comment. We
> shouldn't be relying on nrseqstate for the number of seq_ctrl registers.

Yeap. I confirmed that. I think it's enough with the nr_seq_ctrl.

Thanks!

> 
> > 
> > > 
> > > > 
> > > > Link: https://developer.arm.com/documentation/ihi0064/latest/ [0]
> > > > Fixes: 2e1cdfe184b5 ("coresight-etm4x: Adding CoreSight ETM4x driver")
> > > > Reviewed-by: Leo Yan <[email-masked]>
> > > > Signed-off-by: Yeoreum Yun <[email-masked]>
> > > > ---
> > > >    .../hwtracing/coresight/coresight-etm4x-core.c | 18 ++++++++++--------
> > > >    .../coresight/coresight-etm4x-sysfs.c          |  2 ++
> > > >    2 files changed, 12 insertions(+), 8 deletions(-)
> > > > 
> > > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > > index 1e3b0344dc00..94b9385e964a 100644
> > > > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > > @@ -542,9 +542,11 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
> > > >    	etm4x_relaxed_write32(csa, config->vissctlr, TRCVISSCTLR);
> > > >    	if (drvdata->nr_pe_cmp)
> > > >    		etm4x_relaxed_write32(csa, config->vipcssctlr, TRCVIPCSSCTLR);
> > > > -	for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > -		etm4x_relaxed_write32(csa, config->seq_ctrl[i], TRCSEQEVRn(i));
> > > > +
> > > >    	if (drvdata->nrseqstate) {
> > > > +		for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > +			etm4x_relaxed_write32(csa, config->seq_ctrl[i], TRCSEQEVRn(i));
> > > > +
> > > >    		etm4x_relaxed_write32(csa, config->seq_rst, TRCSEQRSTEVR);
> > > >    		etm4x_relaxed_write32(csa, config->seq_state, TRCSEQSTR);
> > > >    	}
> > > > @@ -1896,10 +1898,10 @@ static int etm4_cpu_save(struct coresight_device *csdev)
> > > >    	if (drvdata->nr_pe_cmp)
> > > >    		state->trcvipcssctlr = etm4x_read32(csa, TRCVIPCSSCTLR);
> > > > -	for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > -		state->trcseqevr[i] = etm4x_read32(csa, TRCSEQEVRn(i));
> > > > -
> > > >    	if (drvdata->nrseqstate) {
> > > > +		for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > +			state->trcseqevr[i] = etm4x_read32(csa, TRCSEQEVRn(i));
> > > > +
> > > >    		state->trcseqrstevr = etm4x_read32(csa, TRCSEQRSTEVR);
> > > >    		state->trcseqstr = etm4x_read32(csa, TRCSEQSTR);
> > > >    	}
> > > > @@ -2009,10 +2011,10 @@ static void etm4_cpu_restore(struct coresight_device *csdev)
> > > >    	if (drvdata->nr_pe_cmp)
> > > >    		etm4x_relaxed_write32(csa, state->trcvipcssctlr, TRCVIPCSSCTLR);
> > > > -	for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > -		etm4x_relaxed_write32(csa, state->trcseqevr[i], TRCSEQEVRn(i));
> > > > -
> > > >    	if (drvdata->nrseqstate) {
> > > > +		for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > +			etm4x_relaxed_write32(csa, state->trcseqevr[i], TRCSEQEVRn(i));
> > > > +
> > > >    		etm4x_relaxed_write32(csa, state->trcseqrstevr, TRCSEQRSTEVR);
> > > >    		etm4x_relaxed_write32(csa, state->trcseqstr, TRCSEQSTR);
> > > >    	}
> > > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > > > index e9eeea6240d5..0e1ad175aa1e 100644
> > > > --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > > > @@ -1395,6 +1395,8 @@ static ssize_t seq_idx_store(struct device *dev,
> > > >    	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > > >    	struct etmv4_config *config = &drvdata->config;
> > > > +	if (!drvdata->nrseqstate)
> > > > +		return -ENOTSUPP;
> > > >    	if (kstrtoul(buf, 16, &val))
> > > >    		return -EINVAL;
> > > >    	if (val >= drvdata->nrseqstate - 1)
> > > 
> > 
> 

-- 
Sincerely,
Yeoreum Yun