pwm: rockchip: Eliminate potential race condition when probing

Commit 48cf973cae33 ("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: 48cf973cae33 ("pwm: rockchip: Avoid glitches on already running PWMs")
Reported-by: Trent Piepho <tpiepho@gmail.com>
Signed-off-by: Simon South <simon@simonsouth.net>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c
index b5bab42..228147e 100644 (file)
--- a/drivers/pwm/pwm-rockchip.c
+++ b/drivers/pwm/pwm-rockchip.c
@@ -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);