From: Simon South <simon@simonsouth.net>
To: tpiepho@gmail.com, thierry.reding@gmail.com,
u.kleine-koenig@pengutronix.de, robin.murphy@arm.com,
lee.jones@linaro.org, heiko@sntech.de, bbrezillon@kernel.org,
david.wu@rock-chips.com, steven.liu@rock-chips.com,
linux-pwm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-rockchip@lists.infradead.org
Cc: simon@simonsouth.net
Subject: [PATCH v4 4/5] pwm: rockchip: Eliminate potential race condition when probing
Date: Tue, 19 Jan 2021 11:12:08 -0500 [thread overview]
Message-ID: <4bf623acf2cae5247f60a6e9765f0755132647e4.1610976129.git.simon@simonsouth.net> (raw)
In-Reply-To: <cover.1610976129.git.simon@simonsouth.net>
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>
---
drivers/pwm/pwm-rockchip.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c
index b5bab427b5de..228147e9bc6e 100644
--- 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);
--
2.30.0
next prev parent reply other threads:[~2021-01-19 18:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 16:12 [PATCH v4 0/5] pwm: rockchip: Eliminate potential race condition when probing Simon South
2021-01-19 16:12 ` [PATCH v4 1/5] pwm: rockchip: Enable APB clock during register access while probing Simon South
2021-01-19 16:12 ` [PATCH v4 2/5] pwm: rockchip: rockchip_pwm_probe(): Remove superfluous clk_unprepare() Simon South
2021-01-19 16:12 ` [PATCH v4 3/5] pwm: rockchip: Replace "bus clk" with "PWM clk" Simon South
2021-01-19 16:12 ` Simon South [this message]
2021-01-19 16:12 ` [PATCH v4 5/5] pwm: rockchip: Enable clock before calling clk_get_rate() Simon South
2021-01-19 19:22 ` Uwe Kleine-König
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