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: Hans de Goede <hdegoede@redhat.com>,
linux-pwm@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>,
linux-acpi@vger.kernel.org
Subject: [PATCH v8 03/17] pwm: lpss: Fix off by one error in base_unit math in pwm_lpss_prepare()
Date: Sun, 30 Aug 2020 14:57:39 +0200 [thread overview]
Message-ID: <20200830125753.230420-4-hdegoede@redhat.com> (raw)
In-Reply-To: <20200830125753.230420-1-hdegoede@redhat.com>
According to the data-sheet the way the PWM controller works is that
each input clock-cycle the base_unit gets added to a N bit counter and
that counter overflowing determines the PWM output frequency.
So assuming e.g. a 16 bit counter this means that if base_unit is set to 1,
after 65535 input clock-cycles the counter has been increased from 0 to
65535 and it will overflow on the next cycle, so it will overflow after
every 65536 clock cycles and thus the calculations done in
pwm_lpss_prepare() should use 65536 and not 65535.
This commit fixes this. Note this also aligns the calculations in
pwm_lpss_prepare() with those in pwm_lpss_get_state().
Note this effectively reverts commit 684309e5043e ("pwm: lpss: Avoid
potential overflow of base_unit"). The next patch in this series really
fixes the potential overflow of the base_unit value.
Fixes: 684309e5043e ("pwm: lpss: Avoid potential overflow of base_unit")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v3:
- Add Fixes tag
- Add Reviewed-by: Andy Shevchenko tag
---
drivers/pwm/pwm-lpss.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c
index 9d965ffe66d1..43b1fc634af1 100644
--- a/drivers/pwm/pwm-lpss.c
+++ b/drivers/pwm/pwm-lpss.c
@@ -93,7 +93,7 @@ static void pwm_lpss_prepare(struct pwm_lpss_chip *lpwm, struct pwm_device *pwm,
* The equation is:
* base_unit = round(base_unit_range * freq / c)
*/
- base_unit_range = BIT(lpwm->info->base_unit_bits) - 1;
+ base_unit_range = BIT(lpwm->info->base_unit_bits);
freq *= base_unit_range;
base_unit = DIV_ROUND_CLOSEST_ULL(freq, c);
@@ -104,8 +104,8 @@ static void pwm_lpss_prepare(struct pwm_lpss_chip *lpwm, struct pwm_device *pwm,
orig_ctrl = ctrl = pwm_lpss_read(pwm);
ctrl &= ~PWM_ON_TIME_DIV_MASK;
- ctrl &= ~(base_unit_range << PWM_BASE_UNIT_SHIFT);
- base_unit &= base_unit_range;
+ ctrl &= ~((base_unit_range - 1) << PWM_BASE_UNIT_SHIFT);
+ base_unit &= (base_unit_range - 1);
ctrl |= (u32) base_unit << PWM_BASE_UNIT_SHIFT;
ctrl |= on_time_div;
--
2.28.0
next prev parent reply other threads:[~2020-08-30 12:58 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-30 12:57 [PATCH v8 00/17] acpi/pwm/i915: Convert pwm-crc and i915 driver's PWM code to use the atomic PWM API Hans de Goede
2020-08-30 12:57 ` [PATCH v8 01/17] ACPI / LPSS: Resume Cherry Trail PWM controller in no-irq phase Hans de Goede
2020-08-30 12:57 ` [PATCH v8 02/17] ACPI / LPSS: Save Cherry Trail PWM ctx registers only once (at activation) Hans de Goede
2020-08-30 12:57 ` Hans de Goede [this message]
2020-08-31 11:01 ` [PATCH v8 03/17] pwm: lpss: Fix off by one error in base_unit math in pwm_lpss_prepare() Thierry Reding
2020-08-30 12:57 ` [PATCH v8 04/17] pwm: lpss: Add range limit check for the base_unit register value Hans de Goede
2020-08-31 11:02 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 05/17] pwm: lpss: Add pwm_lpss_prepare_enable() helper Hans de Goede
2020-08-31 11:03 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 06/17] pwm: lpss: Use pwm_lpss_restore() when restoring state on resume Hans de Goede
2020-08-31 11:10 ` Thierry Reding
2020-08-31 11:46 ` Hans de Goede
2020-08-31 13:15 ` Thierry Reding
2020-08-31 17:57 ` Hans de Goede
2020-09-01 8:09 ` Andy Shevchenko
2020-08-30 12:57 ` [PATCH v8 07/17] pwm: lpss: Always update state and set update bit Hans de Goede
2020-08-31 8:56 ` Andy Shevchenko
2020-08-31 11:50 ` Hans de Goede
2020-08-31 11:13 ` Thierry Reding
2020-08-31 11:26 ` Hans de Goede
2020-08-31 13:31 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 08/17] pwm: crc: Fix period / duty_cycle times being off by a factor of 256 Hans de Goede
2020-08-31 11:13 ` Thierry Reding
2020-08-31 11:14 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 09/17] pwm: crc: Fix off-by-one error in the clock-divider calculations Hans de Goede
2020-08-31 11:15 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 10/17] pwm: crc: Fix period changes not having any effect Hans de Goede
2020-08-31 11:15 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 11/17] pwm: crc: Enable/disable PWM output on enable/disable Hans de Goede
2020-08-31 11:16 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 12/17] pwm: crc: Implement apply() method to support the new atomic PWM API Hans de Goede
2020-08-31 11:17 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 13/17] pwm: crc: Implement get_state() method Hans de Goede
2020-08-31 11:18 ` Thierry Reding
2020-08-30 12:57 ` [PATCH v8 14/17] drm/i915: panel: Add get_vbt_pwm_freq() helper Hans de Goede
2020-08-30 12:57 ` [PATCH v8 15/17] drm/i915: panel: Honor the VBT PWM frequency for devs with an external PWM controller Hans de Goede
2020-08-30 12:57 ` [PATCH v8 16/17] drm/i915: panel: Honor the VBT PWM min setting " Hans de Goede
2020-08-30 12:57 ` [PATCH v8 17/17] drm/i915: panel: Use atomic PWM API " Hans de Goede
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