linux-kernel - Re: [PATCH v6 1/4] gpio: mvebu: Add limited PWM support

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Message-ID: <20170530165101.73ae0bf6@gmail.com>
Date:   Tue, 30 May 2017 16:51:01 +0200
From:   Ralph Sennhauser <ralph.sennhauser@...il.com>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "linux-gpio\@vger.kernel.org" <linux-gpio@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Alexandre Courbot <gnurou@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "linux-pwm\@vger.kernel.org" <linux-pwm@...r.kernel.org>,
        "devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel\@lists.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Richard Genoud <richard.genoud@...il.com>
Subject: Re: [PATCH v6 1/4] gpio: mvebu: Add limited PWM support

On Tue, 30 May 2017 15:40:00 +0200
Gregory CLEMENT <gregory.clement@...e-electrons.com> wrote:

> Hi Ralph and Linus,
> 
> I resurrect this thread following the series post by Richard Genoud:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2017-May/509461.html
> 
>  On lun., avril 24 2017, Linus Walleij <linus.walleij@...aro.org>
> wrote:
> 
> > On Fri, Apr 14, 2017 at 5:40 PM, Ralph Sennhauser
> > <ralph.sennhauser@...il.com> wrote:
> >  
> >> From: Andrew Lunn <andrew@...n.ch>
> >>
> >> Armada 370/XP devices can 'blink' GPIO lines with a configurable on
> >> and off period. This can be modelled as a PWM.
> >>
> >> However, there are only two sets of PWM configuration registers for
> >> all the GPIO lines. This driver simply allows a single GPIO line
> >> per GPIO chip of 32 lines to be used as a PWM. Attempts to use
> >> more return EBUSY.
> >>
> >> Due to the interleaving of registers it is not simple to separate
> >> the PWM driver from the GPIO driver. Thus the GPIO driver has been
> >> extended with a PWM driver.
> >>
> >> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> >> URL: https://patchwork.ozlabs.org/patch/427287/
> >> URL: https://patchwork.ozlabs.org/patch/427295/
> >> [Ralph Sennhauser:
> >>   * Port forward
> >>   * Merge PWM portion into gpio-mvebu.c
> >>   * Switch to atomic PWM API
> >>   * Add new compatible string marvell,armada-370-xp-gpio  
> 
> The fact that Richard managed to run the code on Armada 38x draw my
> attention on the documentation that need to be amend.

Hi Gregory

But does it behave as a pwm-fan? I don't have access to the 38x
functional spec (no NDA with Marvell), the one for XP is public.
According to Andrew the 38x doesn't have the blinking hardware and so I
expect the pwm-fan is just an overblown gpio-fan there, additionally
writing some random values to random registers where luck has it nothing
goes wrong.

Kirkwood apparently has blinking support but only at fixed frequency of
10Hz, so not usable for this purpose either.

So to my knowledge it really is just 370 and XP.

> 
> And it makes me realized that I missed the bad naming of the
> compatible string. We don't use family name for the compatible
> string, but the name of the first SoC compatible with. So in this
> case we should use "marvell,armada-370", as it is still in rc and not
> yet deployed. What about fixing the name now?

I don't mind but certainly not for me to decide at this point.

> 
> I can send a patch for it if you want and fix the dts that are still
> in my mvebu branch.

Sure, or if you prefer I can do it as well if we decide for the change.
No preference.

Ralph