Commit d21ba5d6 authored by Simon South's avatar Simon South Committed by Thierry Reding
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pwm: rockchip: Eliminate potential race condition when probing 



Commit 48cf973c ("pwm: rockchip: Avoid glitches on already running
PWMs") introduced a potential race condition in rockchip_pwm_probe(): A
consumer could enable an inactive PWM, or disable a running one, between
rockchip_pwm_probe() registering the device via pwmchip_add() and checking
whether it is enabled (to determine whether it was started by a
bootloader). This could result in a device's PWM clock being either enabled
once more than necessary, potentially causing it to continue running when
no longer needed, or disabled once more than necessary, producing a warning
from the kernel.

Eliminate these possibilities by modifying rockchip_pwm_probe() so it
checks whether a device is enabled before registering it rather than after.

Fixes: 48cf973c ("pwm: rockchip: Avoid glitches on already running PWMs")
Reported-by: default avatarTrent Piepho <tpiepho@gmail.com>
Signed-off-by: default avatarSimon South <simon@simonsouth.net>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent c9f809d0

drivers/pwm/pwm-rockchip.c

+6 −3
Original line number Diff line number Diff line
@@ -288,6 +288,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev) 
	const struct of_device_id *id;

	struct rockchip_pwm_chip *pc;

	u32 enable_conf, ctrl;

	bool enabled;

	int ret, count;



	id = of_match_device(rockchip_pwm_dt_ids, &pdev->dev);
@@ -349,6 +350,10 @@ static int rockchip_pwm_probe(struct platform_device *pdev) 
		pc->chip.of_pwm_n_cells = 3;

	}



	enable_conf = pc->data->enable_conf;

	ctrl = readl_relaxed(pc->base + pc->data->regs.ctrl);

	enabled = (ctrl & enable_conf) == enable_conf;



	ret = pwmchip_add(&pc->chip);

	if (ret < 0) {

		dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
@@ -356,9 +361,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev) 
	}



	/* Keep the PWM clk enabled if the PWM appears to be up and running. */

	enable_conf = pc->data->enable_conf;

	ctrl = readl_relaxed(pc->base + pc->data->regs.ctrl);

	if ((ctrl & enable_conf) != enable_conf)

	if (!enabled)

		clk_disable(pc->clk);



	clk_disable(pc->pclk);