Re: [PATCH v2 0/6] Support PWM polarity control
From: Lukasz Majewski
Date: Thu Oct 06 2016 - 03:06:05 EST
> 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 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.
> >>  http://thread.gmane.org/gmane.linux.pwm/1621
> >>  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)
#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,
> > Could you check on your setup if similar situation takes place? I
> > mean if the brightness control works as expected?
> > Thanks in advance,
> > Åukasz 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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