Re: [PATCH 3/3] HID: multitouch: Disable event reporting on suspend when our parent is not a wakeup-source

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 5/5/21 3:40 PM, Benjamin Tissoires wrote:
> Hi Hans,
> 
> On Sat, Mar 6, 2021 at 2:37 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> Disable event reporting on suspend when our parent is not
>> a wakeup-source. This should help save some extra power in
>> this case.
>>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>>  drivers/hid/Kconfig          |  2 +-
>>  drivers/hid/hid-multitouch.c | 23 ++++++++++++++++++++++-
>>  2 files changed, 23 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
>> index 786b71ef7738..5cbe4adfd816 100644
>> --- a/drivers/hid/Kconfig
>> +++ b/drivers/hid/Kconfig
>> @@ -675,7 +675,7 @@ config HID_MONTEREY
>>
>>  config HID_MULTITOUCH
>>         tristate "HID Multitouch panels"
>> -       depends on HID
>> +       depends on USB_HID
> 
> I tried really hard during the past 8 years to not have a usbhid
> dependency on hid-multitouch.
> 
> The code below should not break the test suite, but still I am not
> that happy about the Kconfig change.
> 
> I don't see an immediate and better way of doing what you are
> achieving here, but maybe you have some magic I did not think about
> that would help to no pull USB_HID with HID_MULTITOUCH.
> 
> FTR, I think the use case of hid-multitouch *without* USB is rather
> non-existent, but there might be some weird systems with I2C only
> (edge computing?).

Interesting how you often manage to pick out the bits of patches
which I'm not 100% happy with myself either. I was thinking the
same thing myself.

We have this: "hid_is_using_ll_driver(hdev, &usb_hid_driver)" check
in various drivers under drivers/hid and so far the dependency fix
of adding a "depends on USB_HID" was not pretty but ok, because it
would be weird to enable those HID drivers on a system without
USB_HID being enabled. But I agree with you that hid-multitouch
is different. So I did try to come up with something better and
failed.

But now that I look at this with fresh eyes I think I see a
nice solution for this.

I propose to add a hid_is_usb_device() helper which is defined
in hid-core.c (1) and this helper would look like this:

bool hid_is_usb_device(struct hid_device *hid)
{
#if IS_ENABLED(CONFIG_USB_HID)
	return hid_is_using_ll_driver(hid, &usb_hid_driver);
#else
	return false;
#endif
}

And then I can use this helper function instead of directly doing
the hid_is_using_ll_driver() check in hid-multitouch.c fixing
this dependency ugliness.

1) hid-core.c is controlled by CONFIG_HID which gets selected at
the Kconfig level by CONFIG_USB_HID so there is no chance of
builtin vs module issues.

As an added bonus I can then also do a follow-up patch-set to
remove more depends on USB_HID stuff by switching to the helper
in other places too.

###

Unrelated but something else which I was wondering about while
working on this patch. 

I think that it might also be useful to change the
mt_parent_may_wake() helper introduced here into a generic
hid_parent_may_wakeup() helper in case we need a similar thing
in other places. I decided it may be best to do that once we
have a second driver needing such a check, but since we're
discussing this anyways, what is your opinion on this ?

Regards,

Hans



>>         help
>>           Generic support for HID multitouch panels.
>>
>> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
>> index cfb68e443ddd..7926295bab81 100644
>> --- a/drivers/hid/hid-multitouch.c
>> +++ b/drivers/hid/hid-multitouch.c
>> @@ -1759,12 +1759,33 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
>>  }
>>
>>  #ifdef CONFIG_PM
>> +
>> +/* Check if the parent which has the power/wakeup* sysfs attributes may wake the hdev */
>> +static bool mt_parent_may_wake(struct hid_device *hdev)
>> +{
>> +       struct device *parent = hdev->dev.parent;
>> +
>> +       /*
>> +        * USB-HID is attached to the usb_interface (our parent), the
>> +        * power/wakeup* attr are part of the usb-device which is its parent.
>> +        */
>> +       if (hid_is_using_ll_driver(hdev, &usb_hid_driver) && parent)
>> +               parent = parent->parent;
>> +
>> +       if (parent)
>> +               return device_may_wakeup(parent);
>> +
>> +       /* Huh? Play it safe and keep reporting events. */
>> +       return true;
>> +}
>> +
>>  static int mt_suspend(struct hid_device *hdev, pm_message_t state)
>>  {
>>         struct mt_device *td = hid_get_drvdata(hdev);
>>
>>         /* High latency is desirable for power savings during S3/S0ix */
>> -       if (td->mtclass.quirks & MT_QUIRK_DISABLE_WAKEUP)
>> +       if ((td->mtclass.quirks & MT_QUIRK_DISABLE_WAKEUP) ||
>> +           !mt_parent_may_wake(hdev))
>>                 mt_set_modes(hdev, HID_LATENCY_HIGH, false, false);
>>         else
>>                 mt_set_modes(hdev, HID_LATENCY_HIGH, true, true);
>> --
>> 2.30.1
>>
>