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SubjectRe: [PATCH v3 3/3] DT: leds: Add Qualcomm Light Pulse Generator binding
On Mon 20 Nov 12:35 PST 2017, Jacek Anaszewski wrote:

> On 11/20/2017 08:58 PM, Bjorn Andersson wrote:
> > On Sun 19 Nov 13:35 PST 2017, Jacek Anaszewski wrote:
> >
> >> Hi Bjorn,
> >>
> >> Thanks for the update.
> >>
> >> On 11/15/2017 08:13 AM, Bjorn Andersson wrote:
> >>> This adds the binding document describing the three hardware blocks
> >>> related to the Light Pulse Generator found in a wide range of Qualcomm
> >>> PMICs.
> >>>
> >>> Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> >>> ---
> >>>
> >>> Changes since v2:
> >>> - Squashed all things into one node
> >>> - Removed quirks from the binding, compatible implies number of channels, their
> >>> configuration etc.
> >>> - Binding describes LEDs connected as child nodes
> >>> - Support describing multi-channel LEDs
> >>> - Change style of the binding document, to match other LED bindings
> >>>
> >>> Changes since v1:
> >>> - Dropped custom pattern properties
> >>> - Renamed cell-index to qcom,lpg-channel to clarify its purpose
> >>>
> >>> .../devicetree/bindings/leds/leds-qcom-lpg.txt | 66 ++++++++++++++++++++++
> >>> 1 file changed, 66 insertions(+)
> >>> create mode 100644 Documentation/devicetree/bindings/leds/leds-qcom-lpg.txt
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/leds/leds-qcom-lpg.txt b/Documentation/devicetree/bindings/leds/leds-qcom-lpg.txt
> >>> new file mode 100644
> >>> index 000000000000..9cee6f9f543c
> >>> --- /dev/null
> >>> +++ b/Documentation/devicetree/bindings/leds/leds-qcom-lpg.txt
> >>> @@ -0,0 +1,66 @@
> >>> +Binding for Qualcomm Light Pulse Generator
> >>> +
> >>> +The Qualcomm Light Pulse Generator consists of three different hardware blocks;
> >>> +a ramp generator with lookup table, the light pulse generator and a three
> >>> +channel current sink. These blocks are found in a wide range of Qualcomm PMICs.
> >>> +
> >>> +Required properties:
> >>> +- compatible: one of:
> >>> + "qcom,pm8916-pwm",
> >>> + "qcom,pm8941-lpg",
> >>> + "qcom,pm8994-lpg",
> >>> + "qcom,pmi8994-lpg",
> >>> + "qcom,pmi8998-lpg",
> >>> +
> >>> +Optional properties:
> >>> +- qcom,power-source: power-source used to drive the output, as defined in the
> >>> + datasheet. Should be specified if the TRILED block is
> >>> + present
> >>
> >> Range of possible values is missing here.
> >>
> >
> > There seems to be a 4-way mux in all variants, but the wiring is
> > different in the different products. E.g. in pm8941 1 represents VPH_PWR
> > while in pmi8994 this is pulled from a dedicated pin named VIN_RGB.
> >
> > Would you like me to list the 4 options for each compatible?
>
> Could you please explain why user would prefer one power source
> over the other? Is it that they have different max current limit?
>

The mux in pm8941 is connected to ground (0V), vph_pwr (3.6V), internal
5V and min(5V, charger). In pmi8994 it's ground, vdd_rgb (a dedicated
pin) and 4.2V. PMI8998 is a slight variation of PMI8994 and I expect
there to be more variants.

So it's different voltage level and, potentially, current limit.

[..]
> One more question regarding TRILED - in your design it will be
> exposed as a single LED class device with one brightness file,
> right? Does it mean that all three LEDs will be applied the
> same brightness after writing it to the sysfs file?
>

Correct, each LED described in DT will become one LED and can have more
than one (any number of) physical channel associated. The current
implementation applies the same brightness (and pattern) to all channels
associated with a LED.

The open question is still how to pass a color from user space, the
brightness_set and pattern_set would need to be modified to map a list
of brightnesses to the individual channels or to adapt the brightness by
some color-modifier(?).


I've tested the driver on single-LEDs and on RGB-leds and it supports
both, the latter with pulse pattern synchronized over the 3 channels.
So I'm hoping that we can move forward with merging the driver with this
limitation and then discuss the RGB interface in LED-class separately.

Regards,
Bjorn

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