Re: [PATCH v3] usb: dwc3: debugfs: Prevent any register access when devices is runtime suspended

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Mar 16, 2023 at 12:28:58PM +0530, Udipto Goswami wrote:
> When the dwc3 device is runtime suspended, various required clocks would
> get disabled and it is not guaranteed that access to any registers would
> work. Depending on the SoC glue, a register read could be as benign as
> returning 0 or be fatal enough to hang the system.
> 
> In order to prevent such scenarios of fatal errors, bail out of debugfs
> function is dwc3 is suspended.
> 
> Signed-off-by: Udipto Goswami <quic_ugoswami@quicinc.com>
> ---
> v3: Replace pr_err to dev_err.
> 
>  drivers/usb/dwc3/debugfs.c | 60 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/debugfs.c b/drivers/usb/dwc3/debugfs.c
> index 850df0e6bcab..4a9d0994f3b4 100644
> --- a/drivers/usb/dwc3/debugfs.c
> +++ b/drivers/usb/dwc3/debugfs.c
> @@ -544,6 +544,12 @@ static int dwc3_link_state_show(struct seq_file *s, void *unused)
>  	u32			reg;
>  	u8			speed;
>  
> +	if (pm_runtime_suspended(dwc->dev)) {
> +		dev_err(dwc->dev,
> +			"Invalid operation, DWC3 suspended!");
> +		return -EINVAL;
> +	}

What prevents the device from being suspened right after you check this?

thanks,

greg k-h