kernel/linux.git/drivers/pwm/core.c, branch v6.18.22

pwm: Ensure ioctl() returns a negative errno on error

2026-01-30T09:32:12+00:00

[ Upstream commit c198b7773ca5bc3bdfb15b85e414fb9a99a5e5ba ] copy_to_user() returns the number of bytes not copied, thus if there is a problem a positive number. However the ioctl callback is supposed to return a negative error code on error. This error is a unfortunate as strictly speaking it became ABI with the introduction of pwm character devices. However I never saw the issue in real life -- I found this by code inspection -- and it only affects an error case where readonly memory is passed to the ioctls or the address mapping changes while the ioctl is active. Also there are already error cases returning negative values, so the calling code must be prepared to see such values already. Fixes: 9c06f26ba5f5 ("pwm: Add support for pwmchip devices for faster and easier userspace access") Signed-off-by: Uwe Kleine-König Link: https://patch.msgid.link/20260119151325.571857-2-u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König Signed-off-by: Sasha Levin

pwm: Use %u to printf unsigned int pwm_chip::npwm and pwm_chip::id

2025-12-18T13:03:00+00:00

[ Upstream commit 5f7ff902e7f324c10f2b64c5ba2e5e2d0bc4e07e ] %u is the right conversion specifier to emit an unsigned int value. Fixes: 62099abf67a2 ("pwm: Add debugfs interface") Fixes: 0360a4873372 ("pwm: Mention PWM chip ID in /sys/kernel/debug/pwm") Signed-off-by: Uwe Kleine-König Link: https://patch.msgid.link/20251006133525.2457171-2-u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König Signed-off-by: Sasha Levin

pwm: Simplify printf to emit chip->npwm in $debugfs/pwm

2025-12-18T13:03:00+00:00

[ Upstream commit 3cf8e55894b51c14f8500cae5e68ed48b1b0f3fd ] Instead of caring to correctly pluralize "PWM device(s)" using (chip->npwm != 1) ? "s" : "" or str_plural(chip->npwm) just simplify the format to not need a plural-s. Signed-off-by: Uwe Kleine-König Link: https://patch.msgid.link/20250926165702.321514-2-u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König Stable-dep-of: 5f7ff902e7f3 ("pwm: Use %u to printf unsigned int pwm_chip::npwm and pwm_chip::id") Signed-off-by: Sasha Levin

pwm: Provide a gpio device for waveform drivers

2025-09-15T09:39:44+00:00

A PWM is a more general concept than an output-only GPIO. When using duty_length = period_length the PWM looks like an active GPIO, with duty_length = 0 like an inactive GPIO. With the waveform abstraction there is enough control over the configuration to ensure that PWMs that cannot generate a constant signal at both levels error out. The pwm-pca9685 driver already provides a gpio chip. When this driver is converted to the waveform callbacks, the gpio part can just be dropped. Signed-off-by: Uwe Kleine-König Reviewed-by: Bartosz Golaszewski Link: https://lore.kernel.org/r/20250717151117.1828585-2-u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König

pwm: Check actual period and duty_cycle for ignored polarity test

2025-09-15T09:39:44+00:00

When a lowlevel driver configures the wrong period that might (historically) be ok if the emitted signal has a 100% relative duty_cycle as that just corresponds to rounding down the duty_cycle to 0 which is an allowed thing to do for a lowlevel driver. Signed-off-by: Uwe Kleine-König Link: https://lore.kernel.org/r/bc511c0250ea2f6390e4209ab1ea9c08a3c18612.1751994988.git.u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König

pwm: Disable PWM_DEBUG check for disabled states

2025-09-15T09:39:44+00:00

When a PWM is requested to be disabled, the result is unspecified, the only intention is to save some power. So skip all checks in this case. All but two checks already only triggered for states with .enabled = true. The first resulted in some false positive diagnostics, the other checked for a condition that depending on hardware might not be implementable. Similar if the lowlevel driver disabled the hardware this might be a valid reaction and with .enabled = false all other state parameters are unreliable, so skip further tests in this case, too. All later usages of .enabled can be assumed to yield true, and so several if conditions can be simplified. Signed-off-by: Uwe Kleine-König Link: https://lore.kernel.org/r/16d29212b09b66c286c1232b1ab0ec0f8d510aae.1751994988.git.u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König

pwm: Fix incorrect variable used in error message

2025-09-15T09:39:43+00:00

The dev_err message is reporting the incorrect return value ret_tohw, it should be reporting the value in ret_fromhw. Fix this by using ret_fromhw instead of ret_tohw. Fixes: 6c5126c6406d ("pwm: Provide new consumer API functions for waveforms") Signed-off-by: Colin Ian King Link: https://lore.kernel.org/r/20250902130348.2630053-1-colin.i.king@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Uwe Kleine-König

pwm: Expose PWM_WFHWSIZE in public header

2025-07-07T06:39:36+00:00

The WFHWSIZE constant defines the maximum size for the hardware-specific waveform representation buffer. It is currently local to drivers/pwm/core.c, which makes it inaccessible to external tools like bindgen. Move the constant to include/linux/pwm.h to make it part of the public API. As part of this change, rename it to PWM_WFHWSIZE to follow standard kernel conventions for namespacing macros in public headers. This allows bindgen to automatically generate a corresponding constant for the Rust PWM abstractions, ensuring the value remains synchronized between the C core and Rust code and preventing future maintenance issues. Signed-off-by: Michal Wilczynski Link: https://lore.kernel.org/r/20250702-rust-next-pwm-working-fan-for-sending-v7-1-67ef39ff1d29@samsung.com Signed-off-by: Uwe Kleine-König

pwm: Add support for pwmchip devices for faster and easier userspace access

2025-07-07T06:39:33+00:00

With this change each pwmchip defining the new-style waveform callbacks can be accessed from userspace via a character device. Compared to the sysfs-API this is faster and allows to pass the whole configuration in a single ioctl allowing atomic application and thus reducing glitches. On an STM32MP13 I see: root@DistroKit:~ time pwmtestperf real 0m 1.27s user 0m 0.02s sys 0m 1.21s root@DistroKit:~ rm /dev/pwmchip0 root@DistroKit:~ time pwmtestperf real 0m 3.61s user 0m 0.27s sys 0m 3.26s pwmtestperf does essentially: for i in 0 .. 50000: pwm_set_waveform(duty_length_ns=i, period_length_ns=50000, duty_offset_ns=0) and in the presence of /dev/pwmchip0 is uses the ioctls introduced here, without that device it uses /sys/class/pwm/pwmchip0. Signed-off-by: Uwe Kleine-König Link: https://lore.kernel.org/r/ad4a4e49ae3f8ea81e23cac1ac12b338c3bf5c5b.1746010245.git.u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König

pwm: Fix invalid state detection

2025-07-07T06:33:44+00:00

Commit 9dd42d019e63 ("pwm: Allow pwm state transitions from an invalid state") intended to allow some state transitions that were not allowed before. The idea is sane and back then I also got the code comment right, but the check for enabled is bogus. This resulted in state transitions for enabled states to be allowed to have invalid duty/period settings and thus it can happen that low-level drivers get requests for invalid states🙄. Invert the check to allow state transitions for disabled states only. Fixes: 9dd42d019e63 ("pwm: Allow pwm state transitions from an invalid state") Signed-off-by: Uwe Kleine-König Link: https://lore.kernel.org/r/20250704172416.626433-2-u.kleine-koenig@baylibre.com Cc: stable@vger.kernel.org Signed-off-by: Uwe Kleine-König