Subject: [PATCH] hwrng: OMAP: Fix assumption that runtime_get_sync will always succeed

From: [email-masked] (Suman Anna)
Date: Fri, 24 Jun 2016 11:35:34 -0500

Hi Nishanth,

On 06/24/2016 10:57 AM, Menon, Nishanth wrote:
> pm_runtime_get_sync does return a error value that must be checked for
> error conditions, else, due to various reasons, the device maynot be
> enabled and the system will crash due to lack of clock to the hardware
> module.
> 
> Before:
> 12.562784] [00000000] *pgd=fe193835
> 12.562792] Internal error: : 1406 [#1] SMP ARM
> [...]
> 12.562864] CPU: 1 PID: 241 Comm: modprobe Not tainted 4.7.0-rc4-next-20160624 #2
> 12.562867] Hardware name: Generic DRA74X (Flattened Device Tree)
> 12.562872] task: ed51f140 ti: ed44c000 task.ti: ed44c000
> 12.562886] PC is at omap4_rng_init+0x20/0x84 [omap_rng]
> 12.562899] LR is at set_current_rng+0xc0/0x154 [rng_core]
> [...]
> 
> After the proper checks:
> [   94.366705] omap_rng 48090000.rng: _od_fail_runtime_resume: FIXME:
> missing hwmod/omap_dev info
> [   94.375767] omap_rng 48090000.rng: Failed to runtime_get device -19
> [   94.382351] omap_rng 48090000.rng: initialization failed.
> 
> Fixes: 665d92fa85b5 ("hwrng: OMAP: convert to use runtime PM")
> Cc: Paul Walmsley <[email-masked]>
> Signed-off-by: Nishanth Menon <[email-masked]>
> ---
> 
> Patch based on: next-20160624
> Issue seen with next-20160624
> Full crash log: http://pastebin.ubuntu.com/17801376/
> 
>  drivers/char/hw_random/omap-rng.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/hw_random/omap-rng.c b/drivers/char/hw_random/omap-rng.c
> index 8a1432e8bb80..f30a1870cb64 100644
> --- a/drivers/char/hw_random/omap-rng.c
> +++ b/drivers/char/hw_random/omap-rng.c
> @@ -384,7 +384,11 @@ static int omap_rng_probe(struct platform_device *pdev)
>  	}
>  
>  	pm_runtime_enable(&pdev->dev);
> -	pm_runtime_get_sync(&pdev->dev);
> +	ret = pm_runtime_get_sync(&pdev->dev);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Failed to runtime_get device: %d\n", ret);
> +		goto err_ioremap;

You need to also add a pm_runtime_put_noidle() on get_sync failures to
balance the device's power usage_count.

regards
Suman

> +	}
>  
>  	ret = (dev->of_node) ? of_get_omap_rng_device_details(priv, pdev) :
>  				get_omap_rng_device_details(priv);
> @@ -435,8 +439,14 @@ static int __maybe_unused omap_rng_suspend(struct device *dev)
>  static int __maybe_unused omap_rng_resume(struct device *dev)
>  {
>  	struct omap_rng_dev *priv = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = pm_runtime_get_sync(dev);
> +	if (ret) {
> +		dev_err(dev, "Failed to runtime_get device: %d\n", ret);
> +		return ret;
> +	}
>  
> -	pm_runtime_get_sync(dev);
>  	priv->pdata->init(priv);
>  
>  	return 0;
>