linux-kernel - Re: [PATCH v2 0/6] Support PWM polarity control

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Message-ID: <20161006082617.54ebf41e@jawa>
Date:   Thu, 6 Oct 2016 08:26:17 +0200
From:   Lukasz Majewski <l.majewski@...ess.pl>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        shawnguo@...nel.org, thierry.reding@...il.com,
        mark.rutland@....com, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        robh+dt@...nel.org, kernel@...gutronix.de, fabio.estevam@....com,
        linux-arm-kernel@...ts.infradead.org, l.majewski@...sung.com
Subject: Re: [PATCH v2 0/6] Support PWM polarity control

Hi Stefan,

> Hi Lukasz,
> 
> On 2016-10-04 00:48, Lukasz Majewski wrote:
> > Dear Bhuvanchandra,
> > 
> > Thank you for your effort to send those patches to ML.
> > 
> >> Changes since v2:
> >>
> >> - Picked the stalled patchset[1] from Lothar Wassmann which adds
> >> the basic support for polarity control on imx-pwm driver and adds
> >> backward compatibility support for devices which does not have
> >> polarity control feature.
> >>
> >> Changes since Lothars v6:
> >>
> >> - Squash Lukasz patch[2].
> >>
> >> [1] http://thread.gmane.org/gmane.linux.pwm/1621
> >> [2] https://www.spinics.net/lists/arm-kernel/msg530818.html
> >>
> >> Bhuvanchandra DV (3):
> >>   arm: dts: imx7: Update #pwm-cells for PWM polarity control
> >>   arm: dts: imx7-colibri: Use pwm polarity control
> >>   arm: dts: imx7-colibri: Use enable-gpios for BL_ON
> >>
> >> Lothar Wassmann (3):
> >>   pwm: print error messages with pr_err() instead of pr_debug()
> >>   pwm: core: make the PWM_POLARITY flag in DTB optional
> >>   pwm: imx: support output polarity inversion
> > 
> > For some reason this patchset works differently than the one
> > developed by Lothar.
> > 
> > The difference is with the brightness level control.
> > 
> > My brightness definition in DTS:
> > 
> >            pwms = <&pwm2 0 5000000 PWM_POLARITY_INVERTED>;
> > 
> >  		brightness-levels = <  0   1   2   3   4   5   6
> > 7   8   9
> > 
> > 					 ..  ............
> > 				    250 251 252 253 254 255>;
> > 		default-brightness-level = <50>;
> > 		enable-gpios = <&gpio1 2 GPIO_ACTIVE_LOW>;
> > 
> 
> If you are using something else than i.MX 7 you also want to update
> the SoC level device tree, specifically change the pwm-cells property:
> #pwm-cells = <3>;

Good point. However, it is declared elsewhere (with pwm2 node)

&pwm2 {
	#pwm-cells = <3>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_pwm2>;
	status = "okay";
};


> 
> 
> > When I go to the backlight sysfs entry:
> > 
> > cd /sys/devices/soc0/backlight/backlight/backlight
> > 
> > It seems like the brightness level control is inverted - i.e. 
> > 'echo 20 > brightness" makes picture on the screen very bright, and 
> > 'echo 200 > brightness' makes the picture diminish.
> > 
> > With my "internal" patches the situation is opposite (and I've
> > checked it with my HW connections).
> 
> Just to check whether the driver actually applies the polarity you can
> add a #define DEBUG at the top of the driver (drivers/pwm/pwm-imx.c)
> and pass ignore_loglevel as kernel command line. This should give you
> "PWM supports output inversion" at startup and a "... polarity set
> to .." message whenever the polarity is set.

The problem is with the Bhuvanchandra original patch.

I will point it out when replying to original patch.

Thanks for support,

Łukasz Majewski

> 
> --
> Stefan
> 
> > 
> > Could you check on your setup if similar situation takes place? I
> > mean if the brightness control works as expected?
> > 
> > Thanks in advance,
> > Łukasz Majewski
> > 
> >>
> >>  Documentation/devicetree/bindings/pwm/imx-pwm.txt |  6 +--
> >>  arch/arm/boot/dts/imx7-colibri.dtsi               | 12 +++++-
> >>  arch/arm/boot/dts/imx7s.dtsi                      |  8 ++--
> >>  drivers/pwm/core.c                                | 31
> >> ++++++++------ drivers/pwm/pwm-imx.c                             |
> >> 51 +++++++++++++++++++++-- 5 files changed, 83 insertions(+), 25
> >> deletions(-)
> >>


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