From: Michael Walle <michael@walle.cc>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org,
linux-pwm@vger.kernel.org, linux-watchdog@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Rob Herring <robh+dt@kernel.org>,
Jean Delvare <jdelvare@suse.com>,
Guenter Roeck <linux@roeck-us.net>,
Lee Jones <lee.jones@linaro.org>,
Thierry Reding <thierry.reding@gmail.com>,
Wim Van Sebroeck <wim@linux-watchdog.org>,
Shawn Guo <shawnguo@kernel.org>, Li Yang <leoyang.li@nxp.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jason Cooper <jason@lakedaemon.net>,
Marc Zyngier <maz@kernel.org>, Mark Brown <broonie@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller
Date: Fri, 07 Aug 2020 09:55:19 +0200 [thread overview]
Message-ID: <92116be9aa56250becc4019c6c7a1538@walle.cc> (raw)
In-Reply-To: <20200807074543.pfbwlhtegl3oc4zp@pengutronix.de>
Am 2020-08-07 09:45, schrieb Uwe Kleine-König:
> On Fri, Aug 07, 2020 at 09:28:31AM +0200, Michael Walle wrote:
>> Hi Uwe, Hi Lee,
>>
>> Am 2020-08-06 10:40, schrieb Uwe Kleine-König:
>> > On Mon, Aug 03, 2020 at 11:35:52AM +0200, Michael Walle wrote:
>> > > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> > > index 7dbcf6973d33..a0d50d70c3b9 100644
>> > > --- a/drivers/pwm/Kconfig
>> > > +++ b/drivers/pwm/Kconfig
>> > > @@ -428,6 +428,16 @@ config PWM_SIFIVE
>> > > To compile this driver as a module, choose M here: the module
>> > > will be called pwm-sifive.
>> > >
>> > > +config PWM_SL28CPLD
>> > > + tristate "Kontron sl28cpld PWM support"
>> > > + select MFD_SIMPLE_MFD_I2C
>> >
>> > Is it sensible to present this option to everyone? Maybe
>> >
>> > depends on SOME_SYMBOL_ONLY_TRUE_ON_SL28CPLD || COMPILE_TEST
>>
>> Because there is now no real MFD driver anymore, there is also
>> no symbol for that. The closest would be ARCH_ARM64 but I don't
>> think that is a good idea.
>>
>> Lee, what do you think about adding a symbol to the MFD, which
>> selects MFD_SIMPLE_MFD_I2C but doesn't enable any C modules?
>>
>> I.e.
>> config MFD_SL28CPLD
>> tristate "Kontron sl28cpld"
>> select MFD_SIMPLE_MFD_I2C
>> help
>> Say yes here to add support for the Kontron sl28cpld board
>> management controller.
>>
>> Then all the other device driver could depend on the MFD_SL28CPLD
>> symbol.
>>
>> [..]
>>
>> > > +static void sl28cpld_pwm_get_state(struct pwm_chip *chip,
>> > > + struct pwm_device *pwm,
>> > > + struct pwm_state *state)
>> > > +{
>> > > + struct sl28cpld_pwm *priv = dev_get_drvdata(chip->dev);
>> > > + unsigned int reg;
>> > > + int prescaler;
>> > > +
>> > > + sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, ®);
>> > > +
>> > > + state->enabled = reg & SL28CPLD_PWM_CTRL_ENABLE;
>> > > +
>> > > + prescaler = FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg);
>> > > + state->period = SL28CPLD_PWM_PERIOD(prescaler);
>> > > +
>> > > + sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, ®);
>> > > + state->duty_cycle = SL28CPLD_PWM_TO_DUTY_CYCLE(reg);
>> >
>> > Should reg be masked to SL28CPLD_PWM_CYCLE_MAX, or is it guaranteed that
>> > the upper bits are zero?
>>
>> Mh, the hardware guarantees that bit7 is zero. So masking with
>> SL28CPLD_PWM_CYCLE_MAX won't buy us much. But what I could think
>> could go wrong is this: someone set the prescaler to != 0 and the
>> duty cycle to a value greater than the max value for this particular
>> prescaler mode. For the above calculations this would result in a
>> duty_cycle greater than the period, if I'm not mistaken.
>>
>> The behavior of the hardware is undefined in that case (at the moment
>> it will be always on, I guess). So this isn't a valid setting.
>> Nevertheless it might happen. So what about the following:
>>
>> state->duty_cycle = min(state->duty_cycle, state->period);
>
> If you care about this: This can also happen (at least shortly) in
> sl28cpld_pwm_apply() as you write SL28CPLD_PWM_CTRL before
> SL28CPLD_PWM_CYCLE there.
It could also happen if it was the other way around, couldn't it?
Changing modes might glitch.
I care more about returning valid values to the PWM core ;)
-michael
next prev parent reply other threads:[~2020-08-07 7:55 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-03 9:35 [PATCH v7 00/13] Add support for Kontron sl28cpld Michael Walle
2020-08-03 9:35 ` [PATCH v7 01/13] mfd: add simple regmap based I2C driver Michael Walle
2020-08-03 9:35 ` [PATCH v7 02/13] dt-bindings: mfd: Add bindings for sl28cpld Michael Walle
2020-08-03 9:35 ` [PATCH v7 03/13] mfd: simple-mfd-i2c: add sl28cpld support Michael Walle
2020-08-03 9:35 ` [PATCH v7 04/13] irqchip: add sl28cpld interrupt controller support Michael Walle
2020-08-03 9:35 ` [PATCH v7 05/13] watchdog: add support for sl28cpld watchdog Michael Walle
2020-08-03 9:35 ` [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller Michael Walle
2020-08-06 8:40 ` Uwe Kleine-König
2020-08-07 7:28 ` Michael Walle
2020-08-07 7:45 ` Uwe Kleine-König
2020-08-07 7:55 ` Michael Walle [this message]
2020-08-07 10:24 ` Uwe Kleine-König
2020-08-10 7:13 ` Lee Jones
2020-08-10 7:31 ` Michael Walle
2020-08-13 7:09 ` Michael Walle
2020-08-13 8:21 ` Lee Jones
2020-08-03 9:35 ` [PATCH v7 07/13] gpio: add support for the sl28cpld GPIO controller Michael Walle
2020-08-03 9:35 ` [PATCH v7 08/13] hwmon: add support for the sl28cpld hardware monitoring controller Michael Walle
2020-08-03 9:35 ` [PATCH v7 09/13] arm64: dts: freescale: sl28: enable sl28cpld Michael Walle
2020-08-03 9:35 ` [PATCH v7 10/13] arm64: dts: freescale: sl28: map GPIOs to input events Michael Walle
2020-08-03 9:35 ` [PATCH v7 11/13] arm64: dts: freescale: sl28: enable LED support Michael Walle
2020-08-03 9:35 ` [PATCH v7 12/13] arm64: dts: freescale: sl28: enable fan support Michael Walle
2020-08-03 9:35 ` [PATCH v7 13/13] arm64: defconfig: enable the sl28cpld board management controller Michael Walle
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