Re: [PATCH 2/2] usb: dwc3: of_simple: don't call pm_runtime_set_active()

[Johan Hovold]

On Mon, May 28, 2018 at 05:36:14PM +0300, Roger Quadros wrote:
> Don't call pm_runtime_set_active() as it will prevent the device
> from being activated in the next pm_runtime_get_sync() call.
> 
> Also call pm_runtime_get_sync() before of_platform_populate().

This paragraph describes what you do, but not why do it.

> Signed-off-by: Roger Quadros <rogerq@xxxxxx>
> ---
>  drivers/usb/dwc3/dwc3-of-simple.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-of-simple.c b/drivers/usb/dwc3/dwc3-of-simple.c
> index e98d221..2cbb5c0 100644
> --- a/drivers/usb/dwc3/dwc3-of-simple.c
> +++ b/drivers/usb/dwc3/dwc3-of-simple.c
> @@ -121,6 +121,9 @@ static int dwc3_of_simple_probe(struct platform_device *pdev)
>  	if (ret)
>  		goto err_resetc_assert;
>  
> +	pm_runtime_enable(dev);
> +	pm_runtime_get_sync(dev);

This breaks runtime pm as you now get a second round of clock enables
which are never balanced on runtime suspend (the clocks are first
enabled in dwc3_of_simple_clk_init() above and with your change again in
dwc3_of_simple_runtime_resume()).

On the other hand, we currently return from probe() with a positive RPM
count so perhaps the RPM callbacks can just be removed altogether (i.e.
unless some other entity drops that count at some point before
remove()).

>  	ret = of_platform_populate(np, NULL, NULL, dev);
>  	if (ret) {
>  		for (i = 0; i < simple->num_clocks; i++) {
> @@ -131,10 +134,6 @@ static int dwc3_of_simple_probe(struct platform_device *pdev)
>  		goto err_resetc_assert;
>  	}
>  
> -	pm_runtime_set_active(dev);
> -	pm_runtime_enable(dev);
> -	pm_runtime_get_sync(dev);
> -
>  	return 0;
>  
>  err_resetc_assert:

Also note that there's currently a use-after-free in remove(), where
pm_runtime_put_sync() is called after the clocks have been put.
Something like the below (untested) patch should fix it.

Johan