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(80.71.140.73.ipv4.parknet.dk. [80.71.140.73]) by smtp.gmail.com with ESMTPSA id x9-20020a170906710900b0073a20469f31sm7270172ejj.41.2022.10.18.02.13.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Oct 2022 02:13:17 -0700 (PDT) From: Emil Renner Berthing To: Thierry Reding , =?utf-8?q?Uwe_Kleine-K=C3=B6n?= =?utf-8?q?ig?= , Palmer Dabbelt , Paul Walmsley , Atish Patra , "Wesley W. Terpstra" Cc: linux-pwm@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v1] pwm: sifive: Always let the first pwm_apply_state succeed Date: Tue, 18 Oct 2022 11:13:16 +0200 Message-Id: <20221018091316.415685-1-emil.renner.berthing@canonical.com> X-Mailer: git-send-email 2.37.2 MIME-Version: 1.0 X-Spam-Status: No, score=-4.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747016252219906222?= X-GMAIL-MSGID: =?utf-8?q?1747016252219906222?= Commit 2cfe9bbec56ea579135cdd92409fff371841904f 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: 9e37a53eb051 ("pwm: sifive: Add a driver for SiFive SoC PWM") Signed-off-by: Emil Renner Berthing --- drivers/pwm/pwm-sifive.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c index 2d4fa5e5fdd4..ccdf92045f34 100644 --- a/drivers/pwm/pwm-sifive.c +++ b/drivers/pwm/pwm-sifive.c @@ -159,7 +159,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, mutex_lock(&ddata->lock); if (state->period != ddata->approx_period) { - if (ddata->user_count != 1) { + if (ddata->user_count != 1 && ddata->approx_period) { mutex_unlock(&ddata->lock); return -EBUSY; }