Patch "hwrng: st - keep clock enabled while hwrng is registered" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    hwrng: st - keep clock enabled while hwrng is registered

to the 5.15-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-st-keep-clock-enabled-while-hwrng-is-registere.patch
and it can be found in the queue-5.15 subdirectory.

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



commit 86e685ed4e0333731d60645171894b5509279973
Author: Martin Kaiser <martin@xxxxxxxxx>
Date:   Fri Jun 16 09:58:13 2023 +0100

    hwrng: st - keep clock enabled while hwrng is registered
    
    [ Upstream commit 501e197a02d4aef157f53ba3a0b9049c3e52fedc ]
    
    The st-rng driver uses devres to register itself with the hwrng core,
    the driver will be unregistered from hwrng when its device goes out of
    scope. This happens after the driver's remove function is called.
    
    However, st-rng's clock is disabled in the remove function. There's a
    short timeframe where st-rng is still registered with the hwrng core
    although its clock is disabled. I suppose the clock must be active to
    access the hardware and serve requests from the hwrng core.
    
    Switch to devm_clk_get_enabled and let devres disable the clock and
    unregister the hwrng. This avoids the race condition.
    
    Fixes: 3e75241be808 ("hwrng: drivers - Use device-managed registration API")
    Signed-off-by: Martin Kaiser <martin@xxxxxxxxx>
    Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
index 15ba1e6fae4d2..6e9dfac9fc9f4 100644
--- a/drivers/char/hw_random/st-rng.c
+++ b/drivers/char/hw_random/st-rng.c
@@ -42,7 +42,6 @@
 
 struct st_rng_data {
 	void __iomem	*base;
-	struct clk	*clk;
 	struct hwrng	ops;
 };
 
@@ -85,26 +84,18 @@ static int st_rng_probe(struct platform_device *pdev)
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
-	clk = devm_clk_get(&pdev->dev, NULL);
+	clk = devm_clk_get_enabled(&pdev->dev, NULL);
 	if (IS_ERR(clk))
 		return PTR_ERR(clk);
 
-	ret = clk_prepare_enable(clk);
-	if (ret)
-		return ret;
-
 	ddata->ops.priv	= (unsigned long)ddata;
 	ddata->ops.read	= st_rng_read;
 	ddata->ops.name	= pdev->name;
 	ddata->base	= base;
-	ddata->clk	= clk;
-
-	dev_set_drvdata(&pdev->dev, ddata);
 
 	ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
 	if (ret) {
 		dev_err(&pdev->dev, "Failed to register HW RNG\n");
-		clk_disable_unprepare(clk);
 		return ret;
 	}
 
@@ -113,15 +104,6 @@ static int st_rng_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static int st_rng_remove(struct platform_device *pdev)
-{
-	struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
-
-	clk_disable_unprepare(ddata->clk);
-
-	return 0;
-}
-
 static const struct of_device_id st_rng_match[] __maybe_unused = {
 	{ .compatible = "st,rng" },
 	{},
@@ -134,7 +116,6 @@ static struct platform_driver st_rng_driver = {
 		.of_match_table = of_match_ptr(st_rng_match),
 	},
 	.probe = st_rng_probe,
-	.remove = st_rng_remove
 };
 
 module_platform_driver(st_rng_driver);