| Message ID | 88a446b3e7f6a9bd1d2c079926fcaa408622e480.1608735481.git.simon@simonsouth.net |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | pwm: rockchip: Eliminate potential race condition when probing | expand |
Hello, On Wed, Dec 23, 2020 at 11:01:06AM -0500, Simon South wrote: > 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. > > Also update the code that handles errors from pwmchip_add() to account for > the fact a device's PWM clock may now be disabled and that its APB clock > certainly is, and eliminate the "err_pclk" goto target as it is no longer > of use. > > 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> > --- > drivers/pwm/pwm-rockchip.c | 22 +++++++++++++--------- > 1 file changed, 13 insertions(+), 9 deletions(-) > > diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c > index 3b1aa5daafff..d904a5d24885 100644 > --- a/drivers/pwm/pwm-rockchip.c > +++ b/drivers/pwm/pwm-rockchip.c > @@ -289,6 +289,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev) > struct rockchip_pwm_chip *pc; > struct resource *r; > u32 enable_conf, ctrl; > + bool enabled; > int ret, count; > > id = of_match_device(rockchip_pwm_dt_ids, &pdev->dev); > @@ -351,24 +352,27 @@ static int rockchip_pwm_probe(struct platform_device *pdev) > pc->chip.of_pwm_n_cells = 3; > } > > - ret = pwmchip_add(&pc->chip); > - if (ret < 0) { > - dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret); > - goto err_pclk; > - } > - > /* 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) > + enabled = ((ctrl & enable_conf) == enable_conf); The outer parenthesis pair isn't necessary, please drop it. > + if (!enabled) > clk_disable(pc->clk); > > clk_disable(pc->pclk); > > + ret = pwmchip_add(&pc->chip); > + if (ret < 0) { > + dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret); > + if (enabled) > + clk_disable(pc->clk); > + clk_unprepare(pc->clk); > + clk_unprepare(pc->pclk); > + return ret; > + } > + If you do the pwmchip_add before the clock disable, you can continue to only have a single and simpler error path. The critical part is to check for the enabled hardware before. Best regards Uwe
diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c index 3b1aa5daafff..d904a5d24885 100644 --- a/drivers/pwm/pwm-rockchip.c +++ b/drivers/pwm/pwm-rockchip.c @@ -289,6 +289,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev) struct rockchip_pwm_chip *pc; struct resource *r; u32 enable_conf, ctrl; + bool enabled; int ret, count; id = of_match_device(rockchip_pwm_dt_ids, &pdev->dev); @@ -351,24 +352,27 @@ static int rockchip_pwm_probe(struct platform_device *pdev) pc->chip.of_pwm_n_cells = 3; } - ret = pwmchip_add(&pc->chip); - if (ret < 0) { - dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret); - goto err_pclk; - } - /* 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) + enabled = ((ctrl & enable_conf) == enable_conf); + if (!enabled) clk_disable(pc->clk); clk_disable(pc->pclk); + ret = pwmchip_add(&pc->chip); + if (ret < 0) { + dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret); + if (enabled) + clk_disable(pc->clk); + clk_unprepare(pc->clk); + clk_unprepare(pc->pclk); + return ret; + } + return 0; -err_pclk: - clk_disable_unprepare(pc->pclk); err_clk: clk_disable_unprepare(pc->clk);
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. Also update the code that handles errors from pwmchip_add() to account for the fact a device's PWM clock may now be disabled and that its APB clock certainly is, and eliminate the "err_pclk" goto target as it is no longer of use. 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> --- drivers/pwm/pwm-rockchip.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-)