Re: [PATCH v2 1/2] leds: Add Intel Cherry Trail Whiskey Cove PMIC LEDs

[Jacek Anaszewski]

On 2/15/19 11:26 PM, Hans de Goede wrote:
> Hi,
>
> On 2/15/19 10:42 PM, Jacek Anaszewski wrote:
> > Hi all,
> >
> > On 2/15/19 12:27 PM, Hans de Goede wrote:
> > > Hi,
> > >
> > > On 15-02-19 00:03, Pavel Machek wrote:
> > > > Hi!
> > > >
> > > > > > > > I suggest that we deal with this special case by adding 3 custom
> > > > > > > > sysfs attributes:
> > > > > > > >
> > > > > > > > 1) "mode" which when read, prints, e.g. :
> > > > > > > > manual [on-when-charging]
> > > > > > >
> > > > > > > While this allows _user on console_ to control everything using 
> > > > > > > echo,
> > > > > > > it is not suitable for applications trying to control LEDs.
> > > > > > >
> > > > > > > As there's nothing special about the case here, I believe we should
> > > > > > > have generic solution here.
> > > > > > >
> > > > > > > My preffered solution would be "hardware" trigger that leaves the 
> > > > > > > LED
> > > > > > > in hardware control.
> > > > > >
> > > > > > As you explained in the parts which I snipped, there are many
> > > > > > devices which have a similar choice for a LED being under hw or
> > > > > > user control. I can see how this looks like a trigger and how we
> > > > > > could use the trigger API for this.
> > > > > >
> > > > > > I believe though, that if we implement a "virtual" (for lack of
> > > > > > a better word) trigger for this, that this should be done in the
> > > > > > LED core. I can envision this working like this:
> > > > > >
> > > > > > 1) Add a:
> > > > > >
> > > > > > hw_control_set(struct led_classdev *led_cdev, bool 
> > > > > > enable_hw_control);
> > > > >
> > > > > Please note that we have support for hw patterns in the pattern 
> > > > > trigger.
> > > > > (see how drivers/leds/leds-sc27xx-bltc.c makes use of it for its
> > > > > breathing pattern).
> > > > > We have also support for hw blinking in timer trigger via blink_set 
> > > > > op.
> > > > >
> > > > > In addition to that there is brightness_hw_changed sysfs attribute
> > > > > with led_classdev_notify_brightness_hw_changed() LED API.
> > > > >
> > > > > Couldn't they be used in concert to support the specific features
> > > > > of the device in question?
> > > >
> > > > I believe main issue here is this:
> > > >
> > > > Hardware can automatically control the LED according to the charging
> > > > status, or it can be used as normal software-controlled LED.
> > > >
> > > > I believe we should use trigger to select if hardware controls it or
> > > > not (and then add driver-specific files to describe the
> > > > details). Other proposal is in the mail thread, too.
> > >
> > > Right, so there are really 2 orthogonal issues here:
> > >
> > > 1) With this hardware the LED is either turned on/off automatically
> > > by the PMIC based on charging state; or it is under user control.
> > >
> > > This is different from the led_classdev_notify_brightness_hw_changed
> > > case, where the hardware may update the state underneath the driver,
> > > but the driver can still always update the state itself. In this case
> > > if the LED is in hw-control mode then the driver cannot turn it on/off.
> > >
> > > Pavel suggested modeling this with a new "hardware' trigger, where
> > > setting the trigger to this trigger will enable the hw-controlled
> > > mode and setting any other trigger will switch thing to the 
> > > user-controlled
> > > mode.
> >
> > We already do have hw_pattern file exposed by pattern trigger.
> > It can be used to set hw breathing mode using some device specific
> > syntax semantics, documented in dedicated ABI documentation.
> > It was introduced for similar case, see
> > Documentation/ABI/testing/sysfs-class-led-driver-sc27xx.
>
> Ah I see, yes that could be used, the pattern would just be a single
> integer specifying the cycle time in milliseconds, as nothing
> else is configurable.

I depends on how the pattern looks like. If it is breathing then
we'd need more than one value.

> I think that should work fine, which means that we can use the timer and
> pattern trigger support for the blinking and breathing modes.
>
> That still leaves the switching between user and hw-control modes,
> as discussed the hw-controlled mode could be modelled as a new "hardware"
> trigger, but then we cannot choose between on/blink/breathing when
> in hw-controlled mode. As Pavel mentioned, that would require some
> sort of composed trigger, where we have both the hardware and
> timer triggers active for example.
>
> I think it might be easier to just allow turning on/off the hardware
> control mode through a special "hardware_control" sysfs attribute and
> then use the existing timer and pattern triggers for blinking / breathing.

Pattern trigger exposes pattern file by default and hw_pattern if
pattern_set/get ops are provided. Writing them enables software and
hardware pattern respectively.

--
Best regards,
Jacek Anaszewski