From: Andrea della Porta <andrea.porta@suse•com>
To: "Uwe Kleine-König" <ukleinek@kernel•org>
Cc: Andrea della Porta <andrea.porta@suse•com>,
linux-pwm@vger•kernel.org, Rob Herring <robh@kernel•org>,
Krzysztof Kozlowski <krzk+dt@kernel•org>,
Conor Dooley <conor+dt@kernel•org>,
Florian Fainelli <florian.fainelli@broadcom•com>,
Broadcom internal kernel review list
<bcm-kernel-feedback-list@broadcom•com>,
devicetree@vger•kernel.org, linux-rpi-kernel@lists•infradead.org,
linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org,
Naushir Patuck <naush@raspberrypi•com>,
Stanimir Varbanov <svarbanov@suse•de>
Subject: Re: [PATCH 2/3] pwm: rp1: Add RP1 PWM controller driver
Date: Fri, 10 Apr 2026 12:27:35 +0200 [thread overview]
Message-ID: <adjQl37-6a--_y3Y@apocalypse> (raw)
In-Reply-To: <adiW1tBC8Imd14LD@monoceros>
Hi Uwe,
On 08:27 Fri 10 Apr , Uwe Kleine-König wrote:
> Hello Andrea,
>
> On Thu, Apr 09, 2026 at 06:16:41PM +0200, Andrea della Porta wrote:
> > On 23:45 Sun 05 Apr , Uwe Kleine-König wrote:
> > > On Fri, Apr 03, 2026 at 04:31:55PM +0200, Andrea della Porta wrote:
> > > > +static void rp1_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > > > +{
> > > > + struct rp1_pwm *rp1 = pwmchip_get_drvdata(chip);
> > > > + u32 value;
> > > > +
> > > > + value = readl(rp1->base + PWM_CHANNEL_CTRL(pwm->hwpwm));
> > > > + value &= ~PWM_MODE_MASK;
> > > > + writel(value, rp1->base + PWM_CHANNEL_CTRL(pwm->hwpwm));
> > > > +
> > > > + rp1_pwm_apply_config(chip, pwm);
> > >
> > > What is the purpose of this call?
> >
> > To update the configuration on the next PWM strobe in order to avoid
> > glitches. I'll add a short comment in the code.
>
> .pwm_free() should not touch the hardware configuration. Changing the
> pinmuxing (which I guess is the purpose of clearing PWM_MODE_MASK) is
> somewhat a grey area. If that saves energy, that's okish. Otherwise
> not interfering with the operation of the PWM (e.g. to keep a display on
> during kexec or so) is preferred.
Sorry I should've been more clear on this. The pinmux/conf is not changed
at all by this mask, only the PWM output mode is. The controller can output
several type of waveforms and clearing PWM_MODE_MASK is just setting the
controller to output a 0, which is the reset default i.e. the same value
as just before exporting the channel.
I guess this is the expected behaviour in case of a fan, it should stop
spinning in case you unexport the pwm channel, but I see it could be
different with displays.
Honestly I don't have a strong opinion about that, please just let me
know if I should drop that pwm_free entirely.
>
> > > > +static int rp1_pwm_resume(struct device *dev)
> > > > +{
> > > > + struct rp1_pwm *rp1 = dev_get_drvdata(dev);
> > > > +
> > > > + return clk_prepare_enable(rp1->clk);
> > >
> > > Hmm, if this fails and then the driver is unbound, the clk operations
> > > are not balanced.
> >
> > I'll add some flags to check if the clock is really enabled or not.
>
> To be honest, I guess that is a problem of several drivers, not only in
> drivers/pwm. If this complicates the driver, I guess addressing this
> isn't very critical.
I'll come up with something, we can always drop this check if deemed
too 'noisy'.
Many thanks,
Andrea
>
> Best regards
> Uwe
next prev parent reply other threads:[~2026-04-10 10:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-03 14:31 [PATCH 0/3] Add RP1 PWM controller support Andrea della Porta
2026-04-03 14:31 ` [PATCH 1/3] dt-bindings: pwm: Add Raspberry Pi RP1 PWM controller Andrea della Porta
2026-04-05 7:52 ` Krzysztof Kozlowski
2026-04-07 8:29 ` Andrea della Porta
2026-04-03 14:31 ` [PATCH 2/3] pwm: rp1: Add RP1 PWM controller driver Andrea della Porta
2026-04-05 21:45 ` Uwe Kleine-König
2026-04-09 16:16 ` Andrea della Porta
2026-04-10 6:27 ` Uwe Kleine-König
2026-04-10 10:27 ` Andrea della Porta [this message]
2026-04-10 10:47 ` Uwe Kleine-König
2026-04-03 14:31 ` [PATCH 3/3] arm64: dts: broadcom: rp1: Add PWM node Andrea della Porta
2026-04-05 7:53 ` Krzysztof Kozlowski
2026-04-05 21:48 ` Uwe Kleine-König
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