[PATCH V2 12/13] i3c: mipi-i3c-hci-pci: Add LTR support for Intel controllers

[Frank Li]

On Mon, Nov 17, 2025 at 07:47:05PM +0200, Adrian Hunter wrote:
> On 17/11/2025 17:59, Frank Li wrote:
> > On Mon, Nov 17, 2025 at 01:36:36PM +0200, Adrian Hunter wrote:
> >> On 14/11/2025 22:09, Frank Li wrote:
> >>> On Fri, Nov 14, 2025 at 08:13:55PM +0200, Adrian Hunter wrote:
> >>>> Add support for Latency Tolerance Reporting (LTR) for Intel controllers.
> >>>>
> >>>> Implement PM ->set_latency_tolerance() callback to set LTR register values.
> >>>> Also expose LTR register values via debugfs.
> >>>>
> >>>> Signed-off-by: Adrian Hunter <adrian.hunter at intel.com>
> >>>> ---
> >>>>
> >>>>
> >>>> Changes in V2:
> >>>>
> >>>> 	Make use of FIELD_PREP()
> >>>> 	Improve handling of values that exceed the maximum
> >>>>
> >>>>
> >>>>  .../master/mipi-i3c-hci/mipi-i3c-hci-pci.c    | 125 ++++++++++++++++++
> >>>>  1 file changed, 125 insertions(+)
> >>>>
> >>> ...
> >>>> +static void intel_ltr_expose(struct device *dev)
> >>>> +{
> >>>> +	dev->power.set_latency_tolerance = intel_ltr_set;
> >>>> +	dev_pm_qos_expose_latency_tolerance(dev);
> >>>> +}
> >>>> +
> >>>> +static void intel_ltr_hide(struct device *dev)
> >>>> +{
> >>>> +	dev_pm_qos_hide_latency_tolerance(dev);
> >>>> +	dev->power.set_latency_tolerance = NULL;
> >>>> +}
> >>>> +
> >>>> +static struct dentry *intel_actualize_debugfs_root(bool add)
> >>>> +{
> >>>> +	static struct dentry *debugfs_root;
> >>>> +	static DEFINE_MUTEX(lock);
> >>>> +	static int ref_cnt;
> >>>> +
> >>>> +	guard(mutex)(&lock);
> >>>> +
> >>>> +	ref_cnt += add ? 1 : -1;
> >>>> +
> >>>> +	if (ref_cnt) {
> >>>> +		if (IS_ERR_OR_NULL(debugfs_root))
> >>>> +			debugfs_root = debugfs_create_dir("intel_i3c", NULL);
> >>>
> >>> I think it'd better to create common "i3c" debugfs root. So your device
> >>> use debugfs_create_dir(dev_name(&hci->pci->dev), ...) under this common
> >>> root.
> >>
> >> The debugfs files are being created for the PCI device to contain PCI
> >> LTR information.  The i3c module has nothing to do with that.
> >>
> >> Also, currently, there is no module dependency between this PCI driver
> >> and i3c, but a dependency would be necessary to coordinate the creation
> >> and deletion of an 'i3c' debugfs directory.
> >>
> >> The extra complexity can't be justified.
> >
> > Don't post new versin before we close open discussion. I see your post
> > patch before this message.
>
> Sorry, but it is late in the release cycle, and it saves time when we
> are in different time zones.
>
> >
> > So, I think not necessary to create to root, which cause complex, (need
> > lock, and refer counter).
>
> So you are OK with V3?

In v3, still create "intel_i3c" root dir, how about direct create dev
under root

	debugfs_create_dir(dev_name(&hci->pci->dev), NULL);

to reduce unneccesary complex, (like mutex lock and ref counter).

Frank

>
> >
> > Frank
> >
> >>
> >>>
> >>> ...
> >>>
> >>>> +
> >>>>  static const struct mipi_i3c_hci_pci_info intel_info = {
> >>>>  	.init = intel_i3c_init,
> >>>> +	.exit = intel_exit,
> >>>>  };
> >>>>
> >>>>  static int mipi_i3c_hci_pci_probe(struct pci_dev *pci,
> >>>> --
> >>>> 2.51.0
> >>>>
> >>>>
> >>>> --
> >>>> linux-i3c mailing list
> >>>> linux-i3c at lists.infradead.org
> >>>> http://lists.infradead.org/mailman/listinfo/linux-i3c
> >>
> >>
> >> --
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> >> http://lists.infradead.org/mailman/listinfo/linux-i3c
>
>
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