linux-kernel - Re: [PATCH v3 2/5] mfd: Add Rockchip mfpwm driver

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Message-ID: <3598089.ElGaqSPkdT@workhorse>
Date: Fri, 31 Oct 2025 13:20:37 +0100
From: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
To: Uwe Kleine-König <ukleinek@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
 Lee Jones <lee@...nel.org>, William Breathitt Gray <wbg@...nel.org>,
 Johan Jonker <jbx6244@...dex.com>
Cc: kernel@...labora.com, Jonas Karlman <jonas@...boo.se>,
 Alexey Charkov <alchark@...il.com>, linux-rockchip@...ts.infradead.org,
 linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org
Subject: Re: [PATCH v3 2/5] mfd: Add Rockchip mfpwm driver

On Tuesday, 28 October 2025 19:52:53 Central European Standard Time Johan Jonker wrote:
> 
> On 10/27/25 18:11, Nicolas Frattaroli wrote:
> > With the Rockchip RK3576, the PWM IP used by Rockchip has changed
> > substantially. Looking at both the downstream pwm-rockchip driver as
> > well as the mainline pwm-rockchip driver made it clear that with all its
> > additional features and its differences from previous IP revisions, it
> > is best supported in a new driver.
> > 
> > This brings us to the question as to what such a new driver should be.
> > To me, it soon became clear that it should actually be several new
> > drivers, most prominently when Uwe Kleine-König let me know that I
> > should not implement the pwm subsystem's capture callback, but instead
> > write a counter driver for this functionality.
> > 
> > Combined with the other as-of-yet unimplemented functionality of this
> > new IP, it became apparent that it needs to be spread across several
> > subsystems.
> > 
> > For this reason, we add a new MFD core driver, called mfpwm (short for
> > "Multi-function PWM"). This "parent" driver makes sure that only one
> > device function driver is using the device at a time, and is in charge
> > of registering the MFD cell devices for the individual device functions
> > offered by the device.
> > 
> > An acquire/release pattern is used to guarantee that device function
> > drivers don't step on each other's toes.
> > 
> > Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
> > ---
> >  MAINTAINERS                        |   2 +
> >  drivers/mfd/Kconfig                |  15 ++
> >  drivers/mfd/Makefile               |   1 +
> >  drivers/mfd/rockchip-mfpwm.c       | 340 +++++++++++++++++++++++++++
> >  include/linux/mfd/rockchip-mfpwm.h | 454 +++++++++++++++++++++++++++++++++++++
> >  5 files changed, 812 insertions(+)
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index baecabab35a2..8f3235ba825e 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -22372,6 +22372,8 @@ L:	linux-rockchip@...ts.infradead.org
> >  L:	linux-pwm@...r.kernel.org
> >  S:	Maintained
> 
> >  F:	Documentation/devicetree/bindings/pwm/rockchip,rk3576-pwm.yaml
> 
> A question not so much for Nicolas specific:
> The yaml documents already have a 'maintainers' entry.
> However MAINTAINERS is full yaml entries.
> Could someone explain why we still need dual registration?
> 
> maintainers:
>   - Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
> 
> > +F:	drivers/soc/rockchip/mfpwm.c
> > +F:	include/soc/rockchip/mfpwm.h
> 
> different file name and location?
> 
>   drivers/mfd/rockchip-mfpwm.c       | 340 +++++++++++++++++++++++++++
>   include/linux/mfd/rockchip-mfpwm.h | 454 +++++++++++++++++++++++++++++++++++++
> 
> 

Yeah, I forgot to adjust this when moving this to being an MFD.
I'll fix it in v4.

> > [... snip ...]
> > diff --git a/drivers/mfd/rockchip-mfpwm.c b/drivers/mfd/rockchip-mfpwm.c
> > new file mode 100644
> > index 000000000000..08c2d8da41b7
> > --- /dev/null
> > +++ b/drivers/mfd/rockchip-mfpwm.c
> > [... snip ...]
> > +
> > +static int mfpwm_register_subdevs(struct rockchip_mfpwm *mfpwm)
> > +{
> > +	int ret;
> > +
> 
> > +	ret = mfpwm_register_subdev(mfpwm, "pwm-rockchip-v4");
> 
> Not sure who came up with this name?

I did.

> In case we need to filter wouldn't be easier to order it just like the bindings: manufacture '-' function

It's based on the filename of the pwm output driver. pwm-rockchip.c
is already taken by v1 to v3 hardware. Apparently however, pwm
subsystem drivers then reverse the order in the driver name, so
`pwm-rockchip.c` registers a driver with the name `rockchip-pwm`.

So I'll rename my PWM output driver to `rockchip-pwm-v4`. The v4
stays, it refers to the hardware IP revision.

> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = mfpwm_register_subdev(mfpwm, "rockchip-pwm-capture");
> > +	if (ret)
> > +		return ret;
> > +
> > +	return 0;
> > +}
> > +
> > [... snip ...]

Kind regards,
Nicolas Frattaroli