Re: [PATCH v2 10/10] pwm: Add Raspberry Pi Firmware based PWM bus

From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: "open list:STAGING SUBSYSTEM" <devel@driverdev.osuosl.org>,
	linux-pwm@vger.kernel.org,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	devicetree <devicetree@vger.kernel.org>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	linux-input <linux-input@vger.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
	"Stefan Wahren" <wahrenst@gmx.net>,
	"Philipp Zabel" <p.zabel@pengutronix.de>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
	"Lee Jones" <lee.jones@linaro.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	"linux-arm Mailing List" <linux-arm-kernel@lists.infradead.org>,
	linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 10/10] pwm: Add Raspberry Pi Firmware based PWM bus
Date: Mon, 26 Oct 2020 15:02:58 +0100	[thread overview]
Message-ID: <13068cff8e3a994df5d8fbe19deb068a741365f3.camel@suse.de> (raw)
In-Reply-To: <CAHp75VcB5oxXs38UH5taVGj21wUi3sHYdRPOj3wxa3yXg0vmUA@mail.gmail.com>

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Hi Andy, thanks for the review!

On Thu, 2020-10-22 at 21:53 +0300, Andy Shevchenko wrote:
> On Thu, Oct 22, 2020 at 9:05 PM Nicolas Saenz Julienne
> <nsaenzjulienne@suse.de> wrote:
> > Adds support to control the PWM bus available in official Raspberry Pi
> > PoE HAT. Only RPi's co-processor has access to it, so commands have to
> > be sent through RPi's firmware mailbox interface.
> >  drivers/pwm/pwm-raspberrypi.c | 221 ++++++++++++++++++++++++++++++++++
> 
> Name is completely confusing.
> Please, make it unique enough to understand that this is exactly the
> device it serves for.
> 
> For example, pwm-rpi-poe is better.

Sounds reasonable, I'll change that.

> 
> ...
> 
> > + *  - Only normal polarity
> 
> Can't it be emulated? Isn't it 100% - duty cycle % ?

I guess it can, OTOH given the rather specific use case, I doubt it'll be
worth the effort.

> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> 
> ...
> 
> > +       ret = rpi_firmware_property(firmware, RPI_FIRMWARE_SET_POE_HAT_VAL,
> > +                                   &msg, sizeof(msg));
> > +       if (ret)
> > +               return ret;
> > +       else if (msg.ret)
> 
> Redundant 'else'

Noted.

> > +       firmware_node = of_get_parent(dev->of_node);
> > +       if (!firmware_node) {
> > +               dev_err(dev, "Missing firmware node\n");
> > +               return -ENOENT;
> > +       }
> > +
> > +       firmware = rpi_firmware_get(firmware_node);
> > +       of_node_put(firmware_node);
> > +       if (!firmware)
> > +               return -EPROBE_DEFER;
> 
> Looks like a hack.

This is the pattern we've been using on all firmware dependent devices so far.
Feel free to suggest a better way, I'll be happy to look into it.

> 
> ...
> 
> > +       ret = pwmchip_remove(&rpipwm->chip);
> > +       if (!ret)
> > +               rpi_firmware_put(rpipwm->firmware);
> > +
> > +       return ret;
> 
> Can't you use the usual pattern?

Yes of course. Don't know why I went this way.

Regards,
Nicolas

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