Subject: Re: [PATCH v5 02/12] coresight: etm4x: fix underflow for nrseqstate

From: Yeoreum Yun <[email-masked]>
Date: Tue, 21 Apr 2026 10:37:08 +0100

Hi Suzuki,

> On 16/04/2026 16:11, Leo Yan wrote:
> > On Wed, Apr 15, 2026 at 05:55:18PM +0100, 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.
> >
> > My suggestion in previous version is not quite right, thanks for
> > making this correct.
> >
> > [...]
> >
> > > @@ -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 -EINVAL;
> >
> > For "nrseqstate = 0" case, would it return -EOPNOTSUPP instead?
>
> Or should we make this only visible if the nrseqstore is meaningful ?

We could by chanige the attributes permission and nullify the store
operation for that device attributes.

Not only this, we can apply similar approach to other sysfs entries too:
  - vinst_pe_cmp_start_stop_store (when nr_pe_cmp == 0)
  - seq_event_reset_store (when nrseqstate == 0)
  - ctxid_pid_store (when !caps->ctxid_size || !caps->numcidc)
  - ctxid_masks_store (when !caps->ctxid_size || !caps->numcidc)

  and others..

Would you like to include those changes in this patchset?
I think it would be better to send seperate patchset..

Thanks!

--
Sincerely,
Yeoreum Yun