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Emil Renner Berthing 334c7b13d3 pwm: sifive: Always let the first pwm_apply_state succeed 
Commit 2cfe9bbec5 added support for the
RGB and green PWM controlled LEDs on the HiFive Unmatched board
managed by the leds-pwm-multicolor and leds-pwm drivers respectively.
All three colours of the RGB LED and the green LED run from different
lines of the same PWM, but with the same period so this works fine when
the LED drivers are loaded one after the other.

Unfortunately it does expose a race in the PWM driver when both LED
drivers are loaded at roughly the same time. Here is an example:

  |          Thread A           |          Thread B           |
  |  led_pwm_mc_probe           |  led_pwm_probe              |
  |    devm_fwnode_pwm_get      |                             |
  |      pwm_sifive_request     |                             |
  |        ddata->user_count++  |                             |
  |                             |    devm_fwnode_pwm_get      |
  |                             |      pwm_sifive_request     |
  |                             |        ddata->user_count++  |
  |         ...                 |          ...                |
  |    pwm_state_apply          |    pwm_state_apply          |
  |      pwm_sifive_apply       |      pwm_sifive_apply       |

Now both calls to pwm_sifive_apply will see that ddata->approx_period,
initially 0, is different from the requested period and the clock needs
to be updated. But since ddata->user_count >= 2 both calls will fail
with -EBUSY, which will then cause both LED drivers to fail to probe.

Fix it by letting the first call to pwm_sifive_apply update the clock
even when ddata->user_count != 1.

Fixes: 9e37a53eb0 ("pwm: sifive: Add a driver for SiFive SoC PWM")
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
2023-01-30 16:42:45 +01:00
arch treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
block treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
certs certs: make system keyring depend on built-in x509 parser 2022-09-24 04:31:18 +09:00
crypto This update includes the following changes: 2022-12-14 12:31:09 -08:00
Documentation kernel hardening fixes for v6.2-rc1 2022-12-23 12:00:24 -08:00
drivers pwm: sifive: Always let the first pwm_apply_state succeed 2023-01-30 16:42:45 +01:00
fs treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
include 9p-for-6.2-rc1 2022-12-23 11:39:18 -08:00
init Kbuild updates for v6.2 2022-12-19 12:33:32 -06:00
io_uring io_uring/net: fix cleanup after recycle 2022-12-19 08:28:28 -07:00
ipc Non-MM patches for 6.2-rc1. 2022-12-12 17:28:58 -08:00
kernel kernel hardening fixes for v6.2-rc1 2022-12-23 12:00:24 -08:00
lib test_maple_tree: add test for mas_spanning_rebalance() on insufficient data 2022-12-21 14:31:52 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm hugetlb: really allocate vma lock for all sharable vmas 2022-12-21 14:31:52 -08:00
net treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
rust rust: types: add Opaque type 2022-12-04 01:59:16 +01:00
samples Char/Misc driver changes for 6.2-rc1 2022-12-16 03:49:24 -08:00
scripts modernize use of grep in coccicheck 2022-12-23 13:56:41 -08:00
security kernel hardening fixes for v6.2-rc1 2022-12-23 12:00:24 -08:00
sound treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
tools perf tools fixes and improvements for v6.2: 2nd batch 2022-12-22 11:07:29 -08:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt ARM64: 2022-12-15 11:12:21 -08:00
.clang-format iommufd for 6.2 2022-12-14 09:15:43 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes
.gitignore kbuild: Cleanup DT Overlay intermediate files as appropriate 2022-11-18 14:45:30 -06:00
.mailmap Non-MM patches for 6.2-rc1. 2022-12-12 17:28:58 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: zram: zsmalloc: Add an additional co-maintainer 2022-12-15 16:37:49 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS io_uring-6.2-2022-12-19 2022-12-21 16:28:25 -08:00
Makefile Linux 6.2-rc1 2022-12-25 13:41:39 -08:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.