| Message ID | 20200830125753.230420-11-hdegoede@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | acpi/pwm/i915: Convert pwm-crc and i915 driver's PWM code to use the atomic PWM API | expand |
On Sun, Aug 30, 2020 at 02:57:46PM +0200, Hans de Goede wrote: > The pwm-crc code is using 2 different enable bits: > 1. bit 7 of the PWM0_CLK_DIV (PWM_OUTPUT_ENABLE) > 2. bit 0 of the BACKLIGHT_EN register > > The BACKLIGHT_EN register at address 0x51 really controls a separate > output-only GPIO which is earmarked to be used as output connected to the > backlight-enable pin for LCD panels, this GPO is part of the PMIC's > "Display Panel Control Block." . This pin should probably be moved over > to a GPIO provider driver (and consumers modified accordingly), but that > is something for an(other) patch. > > Enabling / disabling the actual PWM output is controlled by the > PWM_OUTPUT_ENABLE bit of the PWM0_CLK_DIV register. > > As the comment in the old code already indicates we must disable the PWM > before we can change the clock divider. But the crc_pwm_disable() and > crc_pwm_enable() calls the old code make for this only change the > BACKLIGHT_EN register; and the value of that register does not matter for > changing the period / the divider. What does matter is that the > PWM_OUTPUT_ENABLE bit must be cleared before a new value can be written. > > This commit modifies crc_pwm_config() to clear PWM_OUTPUT_ENABLE instead > when changing the period, so that period changes actually work. > > Note this fix will cause a significant behavior change on some devices > using the CRC PWM output to drive their backlight. Before the PWM would > always run with the output frequency configured by the BIOS at boot, now > the period time specified by the i915 driver will actually be honored. > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Signed-off-by: Hans de Goede <hdegoede@redhat.com> > --- > drivers/pwm/pwm-crc.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) Acked-by: Thierry Reding <thierry.reding@gmail.com>
diff --git a/drivers/pwm/pwm-crc.c b/drivers/pwm/pwm-crc.c index 44ec7d5b63e1..81232da0c767 100644 --- a/drivers/pwm/pwm-crc.c +++ b/drivers/pwm/pwm-crc.c @@ -82,14 +82,11 @@ static int crc_pwm_config(struct pwm_chip *c, struct pwm_device *pwm, if (pwm_get_period(pwm) != period_ns) { int clk_div = crc_pwm_calc_clk_div(period_ns); - /* changing the clk divisor, need to disable fisrt */ - crc_pwm_disable(c, pwm); + /* changing the clk divisor, clear PWM_OUTPUT_ENABLE first */ + regmap_write(crc_pwm->regmap, PWM0_CLK_DIV, 0); regmap_write(crc_pwm->regmap, PWM0_CLK_DIV, clk_div | PWM_OUTPUT_ENABLE); - - /* enable back */ - crc_pwm_enable(c, pwm); } /* change the pwm duty cycle */