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From: Hans de Goede <hdegoede@redhat.com>
To: "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>
Cc: linux-pwm@vger.kernel.org, linux-acpi@vger.kernel.org,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel@lists.freedesktop.org,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: [Intel-gfx] [PATCH v5 09/16] pwm: crc: Fix period changes not having any effect
Date: Fri, 17 Jul 2020 15:37:46 +0200
Message-ID: <20200717133753.127282-10-hdegoede@redhat.com> (raw)
In-Reply-To: <20200717133753.127282-1-hdegoede@redhat.com>

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.

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

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  parent reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 13:37 [Intel-gfx] [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 ` [Intel-gfx] [PATCH v5 01/16] ACPI / LPSS: Resume Cherry Trail PWM controller in no-irq phase Hans de Goede
2020-07-17 13:37 ` [Intel-gfx] [PATCH v5 02/16] ACPI / LPSS: Save Cherry Trail PWM ctx registers only once (at activation) Hans de Goede
2020-07-17 13:37 ` [Intel-gfx] [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 ` [Intel-gfx] [PATCH v5 04/16] pwm: lpss: Add range limit check for the base_unit register value Hans de Goede
2020-07-17 13:37 ` [Intel-gfx] [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 ` [Intel-gfx] [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 ` [Intel-gfx] [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 ` [Intel-gfx] [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 ` Hans de Goede [this message]
2020-07-29 10:30   ` [Intel-gfx] [PATCH v5 09/16] pwm: crc: Fix period changes not having any effect Andy Shevchenko
2020-07-17 13:37 ` [Intel-gfx] [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 ` [Intel-gfx] [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 ` [Intel-gfx] [PATCH v5 12/16] pwm: crc: Implement get_state() method Hans de Goede
2020-07-17 13:37 ` [Intel-gfx] [PATCH v5 13/16] drm/i915: panel: Add get_vbt_pwm_freq() helper Hans de Goede
2020-07-17 13:37 ` [Intel-gfx] [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 ` [Intel-gfx] [PATCH v5 15/16] drm/i915: panel: Honor the VBT PWM min setting " Hans de Goede
2020-07-17 13:44   ` [Intel-gfx] [PATCH v5 16/16] drm/i915: panel: Use atomic PWM API " Hans de Goede
2020-07-27  7:41 ` [Intel-gfx] [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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