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

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

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@...e.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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