Re: [RESEND PATCH v5 0/9] extend PWM framework to support PWM modes

From: Nicolas Ferre
Date: Fri Sep 14 2018 - 12:21:05 EST


On 28/08/2018 at 15:01, Claudiu Beznea wrote:

Please give feedback on these patches which extends the PWM framework in
order to support multiple PWM modes of operations. This series is a rework
of [1] and [2].

This series started with a RFC back on 5 April 2017 "extend PWM framework to support PWM modes". The continuous work starting with v2 of this series on January 12, 2018.

Then Claudiu tried to address all comments up to v4 which didn't have any more reviews. He posted a v5 without comments since May 22, 2018. This series is basically a resent of the v5 (as said in the $subject).

We would like to know what is preventing this series to be included in the PWM sub-system. Note that if some issue still remain with it, we are ready to help to solve them.

Without feedback from you side, we fear that we would miss a merge window again for no obvious reason (DT part is Acked by Rob: patch 5/9).

Best regards,

The current patch series add the following PWM modes:
- PWM mode normal
- PWM mode complementary
- PWM mode push-pull

Normal mode - for PWM channels with one output; output waveforms looks like
__ __ __ __
PWM __| |__| |__| |__| |__

Where T is the signal period

Since PWMs with more than one output per channel could be used as one
output PWM the normal mode is the default mode for all PWMs (if not
specified otherwise).

Complementary mode - for PWM channels with two outputs; output waveforms
for a PWM channel in complementary mode looks line this:
__ __ __ __
PWMH1 __| |__| |__| |__| |__
__ __ __ __ __
PWML1 |__| |__| |__| |__|

Where T is the signal period.

Push-pull mode - for PWM channels with two outputs; output waveforms for a
PWM channel in push-pull mode with normal polarity looks like this:
__ __
PWMH __| |________| |________
__ __
PWML ________| |________| |__

If polarity is inversed:
__ ________ ________
PWMH |__| |__|
________ ________ __
PWML |__| |__|

Where T is the signal period.

The PWM working modes are per PWM channel registered as PWM's capabilities.
The driver registers itself to PWM core a get_caps() function, in
struct pwm_ops, that will be used by PWM core to retrieve PWM capabilities.
If this function is not registered in driver's probe, a default function
will be used to retrieve PWM capabilities. Currently, the default
capabilities includes only PWM normal mode.

PWM state has been updated to keep PWM mode. PWM mode could be configured
via sysfs or via DT. pwm_apply_state() will do the preliminary validation
for PWM mode to be applied.

In sysfs, user could get PWM modes by reading mode file of PWM device:
root@sama5d2-xplained:/sys/class/pwm/pwmchip0/pwm2# ls -l
total 0
-r--r--r-- 1 root root 4096 Oct 9 09:07 capture
lrwxrwxrwx 1 root root 0 Oct 9 09:07 device -> ../../pwmchip0
-rw-r--r-- 1 root root 4096 Oct 9 08:42 duty_cycle
-rw-r--r-- 1 root root 4096 Oct 9 08:44 enable
--w------- 1 root root 4096 Oct 9 09:07 export
-rw-r--r-- 1 root root 4096 Oct 9 08:43 mode
-r--r--r-- 1 root root 4096 Oct 9 09:07 npwm
-rw-r--r-- 1 root root 4096 Oct 9 08:42 period
-rw-r--r-- 1 root root 4096 Oct 9 08:44 polarity
drwxr-xr-x 2 root root 0 Oct 9 09:07 power
lrwxrwxrwx 1 root root 0 Oct 9 09:07 subsystem -> ../../../../../../../../class/pwm
-rw-r--r-- 1 root root 4096 Oct 9 08:42 uevent
--w------- 1 root root 4096 Oct 9 09:07 unexport
root@sama5d2-xplained:/sys/class/pwm/pwmchip0/pwm2# cat mode
normal complementary [push-pull]

The mode enclosed in bracket is the currently active mode.

The mode could be set, via sysfs, by writing to mode file one of the modes
displayed at read:
root@sama5d2-xplained:/sys/class/pwm/pwmchip0/pwm2# echo normal > mode
root@sama5d2-xplained:/sys/class/pwm/pwmchip0/pwm2# cat mode
[normal] complementary push-pull

The PWM push-pull mode could be usefull in applications like half bridge

This series also add PWM modes support for Atmel/Microchip SoCs.

Thank you,
Claudiu Beznea


Changes in v5:
- solved kbuild errors by removing dummy functions for case where
CONFIG_PWM is not defined; adopted this approach since the removed
function are used only when CONFIG_PWM is defined (in PWM core
and few drivers from drivers/pwm/ directory)

Changes in v4:
- removed changes related to pwm_config() as per maintainer proposals
- added pwm_mode_get_valid() to retrieve a valid PWM mode fror PWM device
instead of using BIT(ffs(caps.mode) - 1) and changed drivers to use
pwm_mode_get_valid() instead of pwm_get_caps() + BIT(ffs(caps.mode) - 1)
(patches 2, 3, 4 from this series)
- renamed PWM_MODE() macro in PWMC_MODE() to avoid conflicts with
pwm-sun4i.c driver ('C' stands for capability)
- removed pwm_caps_valid() function

Changes in v3:
- removed changes related to only one of_xlate function for all PWM drivers
- switch to PWM capabilities per PWM channel nor per PWM chip
- squash documentation and bindings patches as requeted by reviewer
- introduced PWM_MODE(name) macro and used a bit enum for pwm modes
- related to DT bindings, used flags cell also for PWM modes
- updated of_xlate specific functions with "state->mode = mode;"
instructions to avoid pwm_apply_state() failures
- use available modes for PWM channel in pwm_config() by first calling
pwm_get_caps() to get caps.modes
- use loops through available modes in mode_store()/mode_show() and also in
of_pwm_xlate_with_flags() instead of "if else" instructions; in this way,
the addition of a new mode is independent of this code sections
- use DTLI=1, DTHI=0 register settings to obtain push-pull mode waveforms
for Atmel/Microchip PWM controller.

Changes in v2:
- remove of_xlate and of_pwm_n_cells and use generic functions to pharse DT
inputs; this is done in patches 1, 2, 3, 4, 5, 6, 7 of this series; this will
make easy the addition of PWM mode support from DT
- add PWM mode normal
- register PWM modes as capabilities of PWM chips at driver probe and, in case
driver doesn't provide these capabilities use default ones
- change the way PWM mode is pharsed via DT by using a new input for pwms
binding property

Claudiu Beznea (9):
pwm: extend PWM framework with PWM modes
pwm: clps711x: populate PWM mode in of_xlate function
pwm: cros-ec: populate PWM mode in of_xlate function
pwm: pxa: populate PWM mode in of_xlate function
pwm: add PWM modes
pwm: atmel: add pwm capabilities
pwm: add push-pull mode support
pwm: add documentation for pwm push-pull mode
pwm: atmel: add push-pull mode support

Documentation/devicetree/bindings/pwm/pwm.txt | 11 ++-
Documentation/pwm.txt | 42 ++++++++-
drivers/pwm/core.c | 125 +++++++++++++++++++++++++-
drivers/pwm/pwm-atmel.c | 118 +++++++++++++++++-------
drivers/pwm/pwm-clps711x.c | 10 ++-
drivers/pwm/pwm-cros-ec.c | 1 +
drivers/pwm/pwm-pxa.c | 1 +
drivers/pwm/sysfs.c | 61 +++++++++++++
include/dt-bindings/pwm/pwm.h | 2 +
include/linux/pwm.h | 64 +++++++++++++
10 files changed, 395 insertions(+), 40 deletions(-)

Nicolas Ferre