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pwm: rockchip: Eliminate potential race condition when probing

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Commit 48cf973cae ("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: 48cf973cae ("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>
This commit is contained in:
Simon South 2021-01-19 11:12:08 -05:00 committed by Thierry Reding
parent c9f809d0db
commit d21ba5d621
1 changed files with 6 additions and 3 deletions
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9
drivers/pwm/pwm-rockchip.c
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@ -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);