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Emil Renner Berthing 094ffaf50b pwm: sifive: Always let the first pwm_apply_state succeed 
[ Upstream commit 334c7b13d3 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-03-11 13:55:17 +01:00
arch MIPS: DTS: CI20: fix otg power gpio 2023-03-10 09:34:30 +01:00
block Revert "blk-cgroup: dropping parent refcount after pd_free_fn() is done" 2023-03-11 11:03:45 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: rsa-pkcs1pad - Use akcipher_request_complete 2023-03-10 09:33:03 +01:00
Documentation mm: memcontrol: deprecate charge moving 2023-03-10 09:34:26 +01:00
drivers pwm: sifive: Always let the first pwm_apply_state succeed 2023-03-11 13:55:17 +01:00
fs f2fs: fix to avoid potential deadlock 2023-03-11 13:55:16 +01:00
include memory: renesas-rpc-if: Split-off private data from struct rpcif 2023-03-11 13:55:17 +01:00
init gcc: disable -Warray-bounds for gcc-11 too 2023-01-14 10:33:43 +01:00
io_uring io_uring: mark task TASK_RUNNING before handling resume/task work 2023-03-10 09:34:07 +01:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel wait: Return number of exclusive waiters awaken 2023-03-10 09:34:34 +01:00
lib sbitmap: Try each queue to wake up at least one waiter 2023-03-10 09:34:34 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm memory tier: release the new_memtier in find_create_memory_tier() 2023-03-10 09:34:27 +01:00
net net/sched: Retire tcindex classifier 2023-03-11 13:55:16 +01:00
rust rust: print: avoid evaluating arguments in pr_* macros in unsafe blocks 2023-02-06 08:06:34 +01:00
samples ftrace: Export ftrace_free_filter() to modules 2023-02-01 08:34:37 +01:00
scripts gcc-plugins: drop -std=gnu++11 to fix GCC 13 build 2023-03-10 09:33:51 +01:00
security ima: Align ima_file_mmap() parameters with mmap_file LSM hook 2023-03-10 09:34:15 +01:00
sound ALSA: hda/realtek: Add quirk for HP EliteDesk 800 G6 Tower PC 2023-03-10 09:34:20 +01:00
tools objtool: Fix memory leak in create_static_call_sections() 2023-03-11 13:55:17 +01:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Register /dev/kvm as the _very_ last thing during initialization 2023-03-10 09:34:11 +01:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.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 .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -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: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
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 audit: update the mailing list in MAINTAINERS 2023-02-25 11:25:42 +01:00
Makefile Linux 6.1.17 2023-03-11 11:03:45 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.