Re: [PATCH v3 0/4] Introduce Allwinner H616 PWM controller

[Richard GENOUD <richard.genoud@bootlin.com>]

Le 23/02/2026 à 21:14, John Stultz a écrit :
> On Fri, Jan 23, 2026 at 1:33 AM Richard Genoud
> <richard.genoud@bootlin.com> wrote:
>>
>> Allwinner H616 PWM controller is quite different from the A10 one.
>>
>> It can drive 6 PWM channels, and like for the A10, each channel has a
>> bypass that permits to output a clock, bypassing the PWM logic, when
>> enabled.
>>
>> But, the channels are paired 2 by 2, sharing a first set of
>> MUX/prescaler/gate.
>> Then, for each channel, there's another prescaler (that will be bypassed
>> if the bypass is enabled for this channel).
>>
>> It looks like that:
>>              _____      ______      ________
>> OSC24M --->|     |    |      |    |        |
>> APB1 ----->| Mux |--->| Gate |--->| /div_m |-----> PWM_clock_src_xy
>>             |_____|    |______|    |________|
>>                            ________
>>                           |        |
>>                        +->| /div_k |---> PWM_clock_x
>>                        |  |________|
>>                        |    ______
>>                        |   |      |
>>                        +-->| Gate |----> PWM_bypass_clock_x
>>                        |   |______|
>> PWM_clock_src_xy -----+   ________
>>                        |  |        |
>>                        +->| /div_k |---> PWM_clock_y
>>                        |  |________|
>>                        |    ______
>>                        |   |      |
>>                        +-->| Gate |----> PWM_bypass_clock_y
>>                            |______|
>>
>> Where xy can be 0/1, 2/3, 4/5
>>
>> PWM_clock_x/y serve for the PWM purpose.
>> PWM_bypass_clock_x/y serve for the clock-provider purpose.
>> The common clock framework has been used to manage those clocks.
>>
>> This PWM driver serves as a clock-provider for PWM_bypass_clocks.
>> This is needed for example by the embedded AC300 PHY which clock comes
>> from PMW5 pin (PB12).
>>
>> Usually, to get a clock from a PWM driver, we use the pwm-clock driver
>> so that the PWM driver doesn't need to be a clk-provider itself.
>> While this works in most cases, here it just doesn't.
>> That's because the pwm-clock request a period from the PWM driver,
>> without any clue that it actually wants a clock at a specific frequency,
>> and not a PWM signal with duty cycle capability.
>> So, the PWM driver doesn't know if it can use the bypass or not, it
>> doesn't even have the real accurate frequency information (23809524 Hz
>> instead of 24MHz) because PWM drivers only deal with periods.
>>
>> With pwm-clock, we loose a precious information along the way (that we
>> actually want a clock and not a PWM signal).
>> That's ok with simple PWM drivers that don't have multiple input clocks,
>> but in this case, without this information, we can't know for sure which
>> clock to use.
>> And here, for instance, if we ask for a 24MHz clock, pwm-clock will
>> requests 42ns (assigned-clocks doesn't help for that matter). The logic
>> is to select the highest clock (100MHz) with no prescaler and a duty
>> cycle value of 2/4 => we have 25MHz instead of 24MHz.
>> And that's a perfectly fine choice for a PMW, because we still can
>> change the duty cycle in the range [0-4]/4.
>> But obviously for a clock, we don't care about the duty cycle, but more
>> about the clock accuracy.
>>
>> And actually, this PWM is really a PWM AND a real clock when the bypass
>> is set.
> 
> During my free/personal time this weekend I was tinkering with Orange
> Pi Zero 2w and was able to use this patch series (along with an
> hdmi-phy patch and some dts changes) to get HDMI working on the
> device.
> I'm eager to see these land!
> 
> Tested-by: John Stultz <jstultz@google.com>

That's great, thanks for testing!

> 
> thanks
> -john
> 


-- 
Richard Genoud, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com