Re: [PATCH v2 0/6] Support PWM polarity control
From: Stefan Agner
Date: Wed Oct 05 2016 - 12:56:17 EST
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>;
> 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.
> 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