Re: [PATCH V2] pwm: imx-tpm: fix kernel crash upon resume due to register access with clocks disabled

["Lothar Waßmann" <LW@KARO-electronics.de>]

If the pwm-imx-tpm driver is being used e.g. for backlight, the
pwm_imx_tpm_apply() function is being called before the device is
resumed and the clocks are enabled, resulting in a data abort:
echo +5 > /sys/class/rtc/rtc0/wakealarm;echo mem > /sys/power/state
PM: suspend entry (deep)
Filesystems sync: 0.006 seconds
Freezing user space processes ... (elapsed 0.015 seconds) done.
OOM killer disabled.
Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
Disabling non-boot CPUs ...
psci: CPU1 killed (polled 0 ms)
Enabling non-boot CPUs ...
Detected VIPT I-cache on CPU1
cacheinfo: Unable to detect cache hierarchy for CPU 1
GICv3: CPU1: found redistributor 100 region 0:0x0000000048060000
CPU1: Booted secondary processor 0x0000000100 [0x412fd050]
CPU1 is up
Internal error: synchronous external abort: 0000000096000010 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 245 Comm: bash Not tainted 6.1.1-karo+g29549c7073bf #1
Hardware name: Ka-Ro electronics GmbH TX93-5210 (NXP i.MX93) module (DT)
pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : pwm_imx_tpm_apply+0x12c/0x3f0
lr : pwm_imx_tpm_apply+0x104/0x3f0
sp : ffff80000a11b710
x29: ffff80000a11b710 x28: 0000000000000001 x27: 0000000000000000
x26: 0000000000000000 x25: 000000000007a12a x24: 0000000000008236
x23: 0000000000000000 x22: ffff00000309b5d0 x21: 0000000000000000
x20: ffff0000022b0a00 x19: ffff00000309b580 x18: 3030387830383231
x17: 0048008800d90326 x16: 0324032303260320 x15: ffff80000a11b780
x14: ffff80000a11b830 x13: ffff80000a11b834 x12: ffff00003fd90740
x11: ffff00000391da00 x10: 00000000000007d0 x9 : ffff80000a11b6b0
x8 : ffff00000391e230 x7 : 0000000000000000 x6 : ffff00000391da00
x5 : 000000001dcd6500 x4 : 0000000000000000 x3 : ffff00000309b5d0
x2 : ffff00000391da00 x1 : 0000000000000000 x0 : ffff800008fdd010
Call trace:
 pwm_imx_tpm_apply+0x12c/0x3f0
 pwm_apply_state+0x5c/0xbc
 pwm_backlight_update_status+0xc4/0x1ac
 drm_panel_enable+0x70/0xe0
[...]

Fix this by remembering the suspend state and returning -EAGAIN in HW
related functions (pwm_imx_tpm_apply() and pwm_imx_tpm_get_state()) as
long as pwm_imx_tpm_resume() has not been called.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
---
V2: one hunk was missing in the first mail
---
 drivers/pwm/pwm-imx-tpm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c
index e5e7b7c339a8..537c7182f988 100644
--- a/drivers/pwm/pwm-imx-tpm.c
+++ b/drivers/pwm/pwm-imx-tpm.c
@@ -64,6 +64,7 @@ struct imx_tpm_pwm_chip {
 	u32 user_count;
 	u32 enable_count;
 	u32 real_period;
+	int suspended;
 };
 
 struct imx_tpm_pwm_param {
@@ -140,6 +141,9 @@ static void pwm_imx_tpm_get_state(struct pwm_chip *chip,
 	u32 rate, val, prescale;
 	u64 tmp;
 
+	if (tpm->suspended)
+		return -EAGAIN;
+
 	/* get period */
 	state->period = tpm->real_period;
 
@@ -294,6 +298,9 @@ static int pwm_imx_tpm_apply(struct pwm_chip *chip,
 	struct pwm_state real_state;
 	int ret;
 
+	if (tpm->suspended)
+		return -EAGAIN;
+
 	ret = pwm_imx_tpm_round_state(chip, &param, &real_state, state);
 	if (ret)
 		return ret;
@@ -397,6 +404,7 @@ static int __maybe_unused pwm_imx_tpm_suspend(struct device *dev)
 	if (tpm->enable_count > 0)
 		return -EBUSY;
 
+	tpm->suspended = 1;
 	clk_disable_unprepare(tpm->clk);
 
 	return 0;
@@ -411,6 +419,7 @@ static int __maybe_unused pwm_imx_tpm_resume(struct device *dev)
 	if (ret)
 		dev_err(dev, "failed to prepare or enable clock: %d\n", ret);
 
+	tpm->suspended = 0;
 	return ret;
 }
 
-- 
2.30.2