The CRC PWM controller has a clock-divider which divides the clock with
a value between 1-128. But as can seen from the PWM_DIV_CLK_xxx
defines, this range maps to a register value of 0-127.
So after calculating the clock-divider we must subtract 1 to get the
register value, unless the requested frequency was so high that the
calculation has already resulted in a (rounded) divider value of 0.
Note that before this fix, setting a period of PWM_MAX_PERIOD_NS which
corresponds to the max. divider value of 128 could have resulted in a
bug where the code would use 128 as divider-register value which would
have resulted in an actual divider value of 0 (and the enable bit being
set). A rounding error stopped this bug from actually happen. This
same rounding error means that after the subtraction of 1 it is impossible
to set the divider to 128. Also bump PWM_MAX_PERIOD_NS by 1 ns to allow
setting a divider of 128 (register-value 127).
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-10-hdegoede@redhat.com
While looking into adding atomic-pwm support to the pwm-crc driver I
noticed something odd, there is a PWM_BASE_CLK define of 6 MHz and
there is a clock-divider which divides this with a value between 1-128,
and there are 256 duty-cycle steps.
The pwm-crc code before this commit assumed that a clock-divider
setting of 1 means that the PWM output is running at 6 MHZ, if that
is true, where do these 256 duty-cycle steps come from?
This would require an internal frequency of 256 * 6 MHz = 1.5 GHz, that
seems unlikely for a PMIC which is using a silicon process optimized for
power-switching transistors. It is way more likely that there is an 8
bit counter for the duty cycle which acts as an extra fixed divider
wrt the PWM output frequency.
The main user of the pwm-crc driver is the i915 GPU driver which uses it
for backlight control. Lets compare the PWM register values set by the
video-BIOS (the GOP), assuming the extra fixed divider is present versus
the PWM frequency specified in the Video-BIOS-Tables:
Device: PWM Hz set by BIOS PWM Hz specified in VBT
Asus T100TA 200 200
Asus T100HA 200 200
Lenovo Miix 2 8 23437 20000
Toshiba WT8-A 23437 20000
So as we can see if we assume the extra division by 256 then the register
values set by the GOP are an exact match for the VBT values, where as
otherwise the values would be of by a factor of 256.
This commit fixes the period / duty_cycle calculations to take the
extra division by 256 into account.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-9-hdegoede@redhat.com
Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation this program is
distributed in the hope that it will be useful but without any
warranty without even the implied warranty of merchantability or
fitness for a particular purpose see the gnu general public license
for more details
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 655 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070034.575739538@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Use pwm_get/set_xxx() helpers instead of directly accessing the pwm->xxx
field. Doing that will ease adaptation of the PWM framework to support
atomic update.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
The Crystalcove PMIC provides three PWM signals and this driver exports
one of them on the BYT platform which is used to control backlight for
DSI panel. This is platform device implementation of the drivers/mfd
cell device for CRC PMIC.
CC: Samuel Ortiz <sameo@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Hans de Goede