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From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Hans de Goede <hdegoede@redhat.com>
Cc: "Thierry Reding" <thierry.reding@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Jani Nikula" <jani.nikula@linux.intel.com>,
	"Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>,
	"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	"Len Brown" <lenb@kernel.org>,
	linux-pwm@vger.kernel.org,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel@lists.freedesktop.org,
	"Mika Westerberg" <mika.westerberg@linux.intel.com>,
	linux-acpi@vger.kernel.org
Subject: Re: [PATCH v5 09/16] pwm: crc: Fix period changes not having any effect
Date: Wed, 29 Jul 2020 13:30:45 +0300
Message-ID: <20200729103045.GQ3703480@smile.fi.intel.com> (raw)
In-Reply-To: <20200717133753.127282-10-hdegoede@redhat.com>

On Fri, Jul 17, 2020 at 03:37:46PM +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
> 
> I strongly suspect that the BACKLIGHT_EN register at address 0x51 really
> controls a separate output-only GPIO which is connected to the LCD panels
> backlight-enable input. Like how the PANEL_EN register at address 0x52
> controls an output-only GPIO which is earmarked for the LCD panel's
> enable pin. If this is correct then this GPIO should really be added to
> the gpio-crystalcove.c driver and the PWM driver should stop poking it.
> But I've been unable to come up with a definitive answer here, so I'm
> keeping this as is for now.
> 
> 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.

We have a confirmation now that those two bits are real GPOs.

So, with corrected commit message

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(-)
> 
> 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 */
> -- 
> 2.26.2
> 

-- 
With Best Regards,
Andy Shevchenko



  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 13:37 [PATCH v5 00/16] acpi/pwm/i915: Convert pwm-crc and i915 driver's PWM code to use the atomic PWM API Hans de Goede
2020-07-17 13:37 ` [PATCH v5 01/16] ACPI / LPSS: Resume Cherry Trail PWM controller in no-irq phase Hans de Goede
2020-07-17 13:37 ` [PATCH v5 02/16] ACPI / LPSS: Save Cherry Trail PWM ctx registers only once (at activation) Hans de Goede
2020-07-17 13:37 ` [PATCH v5 03/16] pwm: lpss: Fix off by one error in base_unit math in pwm_lpss_prepare() Hans de Goede
2020-07-17 13:37 ` [PATCH v5 04/16] pwm: lpss: Add range limit check for the base_unit register value Hans de Goede
2020-07-17 13:37 ` [PATCH v5 05/16] pwm: lpss: Add pwm_lpss_prepare_enable() helper Hans de Goede
2020-07-28 18:45   ` Andy Shevchenko
2020-07-28 19:49     ` Hans de Goede
2020-07-17 13:37 ` [PATCH v5 06/16] pwm: lpss: Use pwm_lpss_apply() when restoring state on resume Hans de Goede
2020-07-28 18:57   ` Andy Shevchenko
2020-07-28 19:55     ` Hans de Goede
2020-07-29  8:12       ` Andy Shevchenko
2020-08-02 20:51         ` Hans de Goede
2020-08-03  8:41           ` Andy Shevchenko
2020-07-17 13:37 ` [PATCH v5 07/16] pwm: crc: Fix period / duty_cycle times being off by a factor of 256 Hans de Goede
2020-07-28 19:36   ` Andy Shevchenko
2020-07-28 20:00     ` Hans de Goede
2020-07-29  8:13   ` Andy Shevchenko
2020-07-17 13:37 ` [PATCH v5 08/16] pwm: crc: Fix off-by-one error in the clock-divider calculations Hans de Goede
2020-07-29 10:28   ` Andy Shevchenko
2020-07-17 13:37 ` [PATCH v5 09/16] pwm: crc: Fix period changes not having any effect Hans de Goede
2020-07-29 10:30   ` Andy Shevchenko [this message]
2020-07-17 13:37 ` [PATCH v5 10/16] pwm: crc: Enable/disable PWM output on enable/disable Hans de Goede
2020-07-29 10:32   ` Andy Shevchenko
2020-07-17 13:37 ` [PATCH v5 11/16] pwm: crc: Implement apply() method to support the new atomic PWM API Hans de Goede
2020-07-29 10:51   ` Andy Shevchenko
2020-07-17 13:37 ` [PATCH v5 12/16] pwm: crc: Implement get_state() method Hans de Goede
2020-07-17 13:37 ` [PATCH v5 13/16] drm/i915: panel: Add get_vbt_pwm_freq() helper Hans de Goede
2020-07-17 13:37 ` [PATCH v5 14/16] drm/i915: panel: Honor the VBT PWM frequency for devs with an external PWM controller Hans de Goede
2020-07-17 13:44 ` [PATCH v5 15/16] drm/i915: panel: Honor the VBT PWM min setting " Hans de Goede
2020-07-17 13:44   ` [PATCH v5 16/16] drm/i915: panel: Use atomic PWM API " Hans de Goede
2020-07-27  7:41 ` [PATCH v5 00/16] acpi/pwm/i915: Convert pwm-crc and i915 driver's PWM code to use the atomic PWM API Thierry Reding
2020-07-29  8:23   ` Andy Shevchenko
2020-07-29  9:32     ` Hans de Goede
2020-07-30  9:26       ` Thierry Reding
2020-08-01 14:33         ` Hans de Goede
2020-07-29 10:54 ` Andy Shevchenko
2020-08-01 14:38   ` Hans de Goede
2020-08-02 11:25     ` Andy Shevchenko
2020-08-02 19:43       ` Hans de Goede

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