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

[Frank Li]

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.

So, I think not necessary to create to root, which cause complex, (need
lock, and refer counter).

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
> >>
> >>
> >> --
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> >> http://lists.infradead.org/mailman/listinfo/linux-i3c
>
>
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