From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: f.fainelli@gmail.com, linux-kernel@vger.kernel.org,
linux-pwm@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com,
linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
wahrenst@gmx.net, linux-input@vger.kernel.org,
dmitry.torokhov@gmail.com, gregkh@linuxfoundation.org,
devel@driverdev.osuosl.org, p.zabel@pengutronix.de,
linux-gpio@vger.kernel.org, linus.walleij@linaro.org,
linux-clk@vger.kernel.org, sboyd@kernel.org,
linux-rpi-kernel@lists.infradead.org, bgolaszewski@baylibre.com,
andy.shevchenko@gmail.com
Subject: Re: [PATCH v7 11/11] pwm: Add Raspberry Pi Firmware based PWM bus
Date: Thu, 11 Mar 2021 14:41:10 +0100 [thread overview]
Message-ID: <865b4bb56cb9b0a9041c61f1ae7c9c76e807ebd3.camel@suse.de> (raw)
In-Reply-To: <20210311131845.x3zybis3x2liu2uk@pengutronix.de>
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On Thu, 2021-03-11 at 14:18 +0100, Uwe Kleine-König wrote:
> Hello Nicolas,
>
> On Thu, Mar 11, 2021 at 02:01:00PM +0100, Nicolas Saenz Julienne wrote:
> > On Wed, 2021-03-10 at 12:50 +0100, Uwe Kleine-König wrote:
> > > On Mon, Jan 18, 2021 at 01:32:44PM +0100, Nicolas Saenz Julienne wrote:
> >
> > [...]
> >
> > > > + /*
> > > > + * This sets the default duty cycle after resetting the board, we
> > > > + * updated it every time to mimic Raspberry Pi's downstream's driver
> > > > + * behaviour.
> > > > + */
> > > > + ret = raspberrypi_pwm_set_property(rpipwm->firmware, RPI_PWM_DEF_DUTY_REG,
> > > > + duty_cycle);
> > > > + if (ret) {
> > > > + dev_err(chip->dev, "Failed to set default duty cycle: %pe\n",
> > > > + ERR_PTR(ret));
> > > > + return ret;
> > >
> > > This only has an effect for the next reboot, right?
> >
> > It effects all reboots until it's further changed.
> >
> > > If so I wonder if it is a good idea in general. (Think: The current PWM
> > > setting enables a motor that makes a self-driving car move at 100 km/h.
> > > Consider the rpi crashes, do I want to car to pick up driving 100 km/h at
> > > power up even before Linux is up again?)
> >
> > I get your point. But this isn't used as a general purpose PWM. For now the
> > interface is solely there to drive a PWM fan that's arguably harmless. This
> > doesn't mean that the RPi foundation will not reuse the firmware interface for
> > other means in the future. In such case we can always use a new DT compatible
> > and bypass this feature (the current DT string is
> > 'raspberrypi,firmware-poe-pwm', which is specific to this use-case).
> >
> > My aim here is to be on par feature wise with RPi's downstream implementation.
>
> Just because the downstream kernel does it should not be the (single)
> reason to do that. My gut feeling is: For a motor restoring the PWM
> config on reboot is bad and for a fan it doesn't really hurt if it
> doesn't restart automatically. So I'd prefer to to drop this feature.
Fair enough, I'll remove it then.
Regards,
Nicolas
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prev parent reply other threads:[~2021-03-11 13:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-18 12:32 [PATCH v7 00/11] Raspberry Pi PoE HAT fan support Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 01/11] firmware: raspberrypi: Keep count of all consumers Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 02/11] firmware: raspberrypi: Introduce devm_rpi_firmware_get() Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 03/11] clk: bcm: rpi: Release firmware handle on unbind Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 04/11] gpio: raspberrypi-exp: " Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 05/11] reset: raspberrypi: " Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 06/11] soc: bcm: raspberrypi-power: " Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 07/11] staging: vchiq: " Nicolas Saenz Julienne
2021-01-26 17:47 ` Greg KH
2021-01-18 12:32 ` [PATCH v7 08/11] input: raspberrypi-ts: Release firmware handle when not needed Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 09/11] dt-bindings: pwm: Add binding for RPi firmware PWM bus Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 10/11] DO NOT MERGE: ARM: dts: Add RPi's official PoE hat support Nicolas Saenz Julienne
2021-01-18 12:32 ` [PATCH v7 11/11] pwm: Add Raspberry Pi Firmware based PWM bus Nicolas Saenz Julienne
2021-02-08 20:53 ` Nicolas Saenz Julienne
2021-03-09 9:59 ` Nicolas Saenz Julienne
2021-03-10 11:50 ` Uwe Kleine-König
2021-03-11 13:01 ` Nicolas Saenz Julienne
2021-03-11 13:18 ` Uwe Kleine-König
2021-03-11 13:41 ` Nicolas Saenz Julienne [this message]
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