Patch "hwrng: stm32 - repair clock handling" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    hwrng: stm32 - repair clock handling

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     hwrng-stm32-repair-clock-handling.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 369ff70c10c83ececb8af3f1212d7fb15aeb0873
Author: Marek Vasut <marex@xxxxxxx>
Date:   Fri Apr 19 07:01:14 2024 +0200

    hwrng: stm32 - repair clock handling
    
    [ Upstream commit c819d7b836c5dfca0854d3e56664293601f2176d ]
    
    The clock management in this driver does not seem to be correct. The
    struct hwrng .init callback enables the clock, but there is no matching
    .cleanup callback to disable the clock. The clock get disabled as some
    later point by runtime PM suspend callback.
    
    Furthermore, both runtime PM and sleep suspend callbacks access registers
    first and disable clock which are used for register access second. If the
    IP is already in RPM suspend and the system enters sleep state, the sleep
    callback will attempt to access registers while the register clock are
    already disabled. This bug has been fixed once before already in commit
    9bae54942b13 ("hwrng: stm32 - fix pm_suspend issue"), and regressed in
    commit ff4e46104f2e ("hwrng: stm32 - rework power management sequences") .
    
    Fix this slightly differently, disable register clock at the end of .init
    callback, this way the IP is disabled after .init. On every access to the
    IP, which really is only stm32_rng_read(), do pm_runtime_get_sync() which
    is already done in stm32_rng_read() to bring the IP from RPM suspend, and
    pm_runtime_mark_last_busy()/pm_runtime_put_sync_autosuspend() to put it
    back into RPM suspend.
    
    Change sleep suspend/resume callbacks to enable and disable register clock
    around register access, as those cannot use the RPM suspend/resume callbacks
    due to slightly different initialization in those sleep callbacks. This way,
    the register access should always be performed with clock surely enabled.
    
    Fixes: ff4e46104f2e ("hwrng: stm32 - rework power management sequences")
    Signed-off-by: Marek Vasut <marex@xxxxxxx>
    Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
index b6182f86d8a4b..0e903d6e22e30 100644
--- a/drivers/char/hw_random/stm32-rng.c
+++ b/drivers/char/hw_random/stm32-rng.c
@@ -363,6 +363,8 @@ static int stm32_rng_init(struct hwrng *rng)
 		return -EINVAL;
 	}
 
+	clk_disable_unprepare(priv->clk);
+
 	return 0;
 }
 
@@ -387,6 +389,11 @@ static int __maybe_unused stm32_rng_runtime_suspend(struct device *dev)
 static int __maybe_unused stm32_rng_suspend(struct device *dev)
 {
 	struct stm32_rng_private *priv = dev_get_drvdata(dev);
+	int err;
+
+	err = clk_prepare_enable(priv->clk);
+	if (err)
+		return err;
 
 	if (priv->data->has_cond_reset) {
 		priv->pm_conf.nscr = readl_relaxed(priv->base + RNG_NSCR);
@@ -468,6 +475,8 @@ static int __maybe_unused stm32_rng_resume(struct device *dev)
 		writel_relaxed(reg, priv->base + RNG_CR);
 	}
 
+	clk_disable_unprepare(priv->clk);
+
 	return 0;
 }