Messages in this thread | | | Date | Mon, 18 Jul 2022 10:27:23 +0200 | Subject | Re: [PATCH v5 13/13] video: backlight: mt6370: Add MediaTek MT6370 support | From | AngeloGioacchino Del Regno <> |
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Il 15/07/22 18:29, Daniel Thompson ha scritto: > On Fri, Jul 15, 2022 at 02:38:45PM +0200, AngeloGioacchino Del Regno wrote: >> Il 15/07/22 13:26, ChiaEn Wu ha scritto: >>> From: ChiaEn Wu <chiaen_wu@richtek.com> >>> >>> MediaTek MT6370 is a SubPMIC consisting of a single cell battery charger >>> with ADC monitoring, RGB LEDs, dual channel flashlight, WLED backlight >>> driver, display bias voltage supply, one general purpose LDO, and the >>> USB Type-C & PD controller complies with the latest USB Type-C and PD >>> standards. >>> >>> This adds support for MediaTek MT6370 Backlight driver. It's commonly used >>> to drive the display WLED. There are 4 channels inside, and each channel >>> supports up to 30mA of current capability with 2048 current steps in >>> exponential or linear mapping curves. >>> >>> Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com> >> >> Hello ChiaEn, >> >> I propose to move this one to drivers/leds (or drivers/pwm) and, instead of >> registering a backlight device, register a PWM device. >> >> This way you will be able to reuse the generic backlight-pwm driver, as you'd >> be feeding the PWM device exposed by this driver to the generic one: this will >> most importantly make it easy to chain it with MTK_DISP_PWM (mtk-pwm-disp) >> with a devicetree that looks like... > > Out of interest, does MT6370 have the same structure for backlights as the prior > systems using mtk-pwm-disp or was mtk-pwm-disp simply a normal(-ish) PWM > that relied on something on the board for all the constant current > driver hardware? > >
As per my understanding, mtk-pwm-disp is chained to other multimedia features of the display block of MediaTek SoCs, such as the AAL (adaptive ambient light), CABC (content adaptive backlight control) etc, other than being a normal(ish) PWM... that's the reason of my request.
Moreover, in the end, this PMIC's backlight controller is just a "fancy" PWM controller, with OCP/OVP.
>> >> pwmleds-disp { >> compatible = "pwm-leds"; >> >> disp_led: disp-pwm { >> label = "backlight-pwm"; >> pwms = <&pwm0 0 500000>; >> max-brightness = <1024>; >> }; >> }; >> >> backlight_lcd0: backlight { >> compatible = "led-backlight"; >> leds = <&disp_led>, <&pmic_bl_led>; >> default-brightness-level = <300>; >> }; > > I think this proposal has to start with the devicetree bindings rather > than the driver. Instead I think the question is: does this proposal > result in DT bindings that better describe the underlying hardware? >
From how I understand it - yes: we have a fancy PWM (&pwm0) that we use to control display backlight (backlight-pwm)...
Obviously, here we're not talking about OLEDs, but LCDs, where the backlight is made of multiple strings of WhiteLED (effectively, a "pwm-leds" controlled "led-backlight").
Using PWM will also allow for a little more fine-grained board specific configuration, as I think that this PMIC (and/or variants of it) will be used in completely different form factors: I think that's going to be both smartphones and tablets/laptops... and I want to avoid vendor properties to configure the PWM part in a somehow different way.
> This device has lots of backlight centric features (OCP, OVP, single > control with multiple outputs, exponential curves, etc) and its not > clear where they would fit into the "PWM" bindings. >
For OCP and OVP, the only bindings that fit would be regulators, but that's not a regulator... and that's about it - I don't really have arguments for that.
What I really want to see here is usage of "generic" drivers like led_bl and/or pwm_bl as to get some "standardization" around with all the benefits that this carries.
> Come to think of it I'm also a little worried also about the whole linear > versus exponential curve thing since I thought LED drivers were required > to use exponential curves. >
That probably depends on how the controller interprets the data, I guess, but I agree with you on this thought.
Regards, Angelo
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