linux-kernel - [PATCH 5.10 403/663] pwm: rockchip: Eliminate potential race condition when probing

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Date:   Mon,  1 Mar 2021 17:10:51 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Trent Piepho <tpiepho@...il.com>,
        Simon South <simon@...onsouth.net>,
        Thierry Reding <thierry.reding@...il.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 403/663] pwm: rockchip: Eliminate potential race condition when probing

From: Simon South <simon@...onsouth.net>

[ Upstream commit d21ba5d6217bd5a6a696678385906ed1994b380b ]

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@...il.com>
Signed-off-by: Simon South <simon@...onsouth.net>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 ede027fbf2bb4..3b8da7b0091b1 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);
@@ -351,6 +352,10 @@ 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);
@@ -358,9 +363,7 @@ 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);
-- 
2.27.0