linux-kernel - Re: [PATCH 2/2] gpio: mvebu: fix gpio bank registration when pwm is used

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Date:   Tue, 30 May 2017 17:14:18 +0200
From:   Ralph Sennhauser <ralph.sennhauser@...il.com>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-pwm@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH 2/2] gpio: mvebu: fix gpio bank registration when pwm is
 used

Hi Richard

On Tue, 30 May 2017 16:45:24 +0200
Richard Genoud <richard.genoud@...il.com> wrote:

> 2017-05-30 15:16 GMT+02:00 Gregory CLEMENT
> <gregory.clement@...e-electrons.com>:
> > Hi Richard,  
> Hi Greg !
> 
> >
> >  On mar., mai 30 2017, Richard Genoud <richard.genoud@...il.com>
> > wrote: 
> >> If more than one gpio bank has the "pwm" property, only one will be
> >> registered successfully, all the others will fail with:
> >> mvebu-gpio: probe of f1018140.gpio failed with error -17
> >>
> >> That's because in alloc_pwms(), the chip->base (aka "int pwm"),
> >> was not set (thus, ==0) ; and 0 is a meaningful start value in
> >> alloc_pwm(). What was intended is chip->base = -1.
> >> Like that, the numbering will be done auto-magically
> >>
> >> Tested on clearfog-pro (Marvell 88F6828)
> >>
> >> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> >> ---
> >>  drivers/gpio/gpio-mvebu.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> >> index cdef2c78cb3b..4734923e11fd 100644
> >> --- a/drivers/gpio/gpio-mvebu.c
> >> +++ b/drivers/gpio/gpio-mvebu.c
> >> @@ -768,6 +768,7 @@ static int mvebu_pwm_probe(struct
> >> platform_device *pdev, mvpwm->chip.dev = dev;
> >>       mvpwm->chip.ops = &mvebu_pwm_ops;
> >>       mvpwm->chip.npwm = mvchip->chip.ngpio;
> >> +     mvpwm->chip.base = -1;  
> >
> > Why not using
> > mvpwm->chip.base = id * MVEBU_MAX_GPIO_PER_BANK;
> > as it is done in the mvebu_gpio_probe() function?  
> Yes, that was my first move:
> mvpwm->chip.base = mvchip->chip.base;
> 
> But after some reflexion, mvpwm->chip.base is not the GPIO base, it's
> the PWM base,
> (mvpwm->chip is a struct pwm_chip), so it would we weird to have
> "holes" in the declared PWMs.
> I'm not clear, so here's an example:
> If, in the DTS, we have:
>             gpio0: gpio@...00 {
>                 compatible = "marvell,armada-370-xp-gpio",
>                          "marvell,orion-gpio";
>                 reg = <0x18100 0x40>, <0x181c0 0x08>;
>                 reg-names = "gpio";  /* "pwm" missing */
> [...]
>             gpio1: gpio@...40 {
>                 compatible = "marvell,armada-370-xp-gpio",
>                          "marvell,orion-gpio";
>                 reg = <0x18140 0x40>, <0x181c8 0x08>;
>                 reg-names = "gpio", "pwm";
> In this case, if gpio0 is not declared as PWM capable, the PWM
> numbering will start at 32 if we have
> mvpwm->chip.base = mvchip->chip.base;
> but it will start at 0 if we have mvpwm->chip.base = -1;
> 
> The pros for having mvpwm->chip.base = mvchip->chip.base; is mainly
> the stable numbering:
> if we add the "pwm" feature to gpio0 afterwards, the pwm numbering in
> sysfs will stay the same.
> And if we have mvpwm->chip.base = -1; the pwm numbering will be
> shifted.
> 
> Looking back at the V5 of this patch
> https://www.spinics.net/lists/kernel/msg2484889.html
> There was the line:
> mvpwm->chip.base = mvchip->chip.base;
> I guess it got lost in the v6 rebase.
> 
> So I could change it back, but I'm not sure which one is better.

Thierry Redding pointed out that the region might already be occupied
by another PWM chip, unlikely but not impossible. That's why it got
changed for v6.

See https://www.spinics.net/lists/devicetree/msg173138.html

Ralph