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

[Adrian Hunter <adrian.hunter@intel.com>]

On 17/11/2025 19:54, Frank Li wrote:
> 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@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).

Could do.  I added intel_i3c to match intel_lpss which is also
PCI devices with LTR e.g.

# tree /sys/kernel/debug/intel_lpss
/sys/kernel/debug/intel_lpss
|-- 0000:00:19.0
|   |-- active_ltr
|   |-- capabilities
|   `-- idle_ltr
`-- 0000:00:19.1
    |-- active_ltr
    |-- capabilities
    `-- idle_ltr

3 directories, 6 files
# tree /sys/kernel/debug/intel_i3c
/sys/kernel/debug/intel_i3c
|-- 0000:00:11.0
|   |-- active_ltr
|   `-- idle_ltr
`-- 0000:00:11.1
    |-- active_ltr
    `-- idle_ltr

3 directories, 4 files
# 


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


-- 
linux-i3c mailing list
linux-i3c@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-i3c