Patch "pwm: sifive: Reduce time the controller lock is held" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    pwm: sifive: Reduce time the controller lock is held

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pwm-sifive-reduce-time-the-controller-lock-is-held.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit fe0a2bdbdc0afda3f6e00e7be647054043a39922
Author: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Date:   Thu Jul 21 12:31:25 2022 +0200

    pwm: sifive: Reduce time the controller lock is held
    
    [ Upstream commit 0f02f491b786143f08eb19840f1cf4f12aec6dee ]
    
    The lock is only to serialize access and update to user_count and
    approx_period between different PWMs served by the same pwm_chip.
    So the lock needs only to be taken during the check if the (chip global)
    period can and/or needs to be changed.
    
    Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
    Tested-by: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
    Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
    Stable-dep-of: 334c7b13d383 ("pwm: sifive: Always let the first pwm_apply_state succeed")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index 538297ef82558..980ddcdd52953 100644
--- a/drivers/pwm/pwm-sifive.c
+++ b/drivers/pwm/pwm-sifive.c
@@ -43,7 +43,7 @@
 
 struct pwm_sifive_ddata {
 	struct pwm_chip	chip;
-	struct mutex lock; /* lock to protect user_count */
+	struct mutex lock; /* lock to protect user_count and approx_period */
 	struct notifier_block notifier;
 	struct clk *clk;
 	void __iomem *regs;
@@ -78,6 +78,7 @@ static void pwm_sifive_free(struct pwm_chip *chip, struct pwm_device *pwm)
 	mutex_unlock(&ddata->lock);
 }
 
+/* Called holding ddata->lock */
 static void pwm_sifive_update_clock(struct pwm_sifive_ddata *ddata,
 				    unsigned long rate)
 {
@@ -166,7 +167,6 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return ret;
 	}
 
-	mutex_lock(&ddata->lock);
 	cur_state = pwm->state;
 	enabled = cur_state.enabled;
 
@@ -185,14 +185,17 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	/* The hardware cannot generate a 100% duty cycle */
 	frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
 
+	mutex_lock(&ddata->lock);
 	if (state->period != ddata->approx_period) {
 		if (ddata->user_count != 1) {
+			mutex_unlock(&ddata->lock);
 			ret = -EBUSY;
 			goto exit;
 		}
 		ddata->approx_period = state->period;
 		pwm_sifive_update_clock(ddata, clk_get_rate(ddata->clk));
 	}
+	mutex_unlock(&ddata->lock);
 
 	writel(frac, ddata->regs + PWM_SIFIVE_PWMCMP0 +
 	       pwm->hwpwm * PWM_SIFIVE_SIZE_PWMCMP);
@@ -202,7 +205,6 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 
 exit:
 	clk_disable(ddata->clk);
-	mutex_unlock(&ddata->lock);
 	return ret;
 }