On Fri, 2 Dec 2016, Todd Brandt wrote:

> Add debug support for experimenting with USB timing delay
> values on the fly. This provides a debug interface through
> /sys/kernel/usb where a user can tweak the values. The code
> enforces the spec minimums so that a user can't set them
> too low.
> 
> Signed-off-by: Todd Brandt <todd.e.bra...@linux.intel.com>
> ---
>  drivers/usb/core/hub.c | 100 
> +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 100 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 43242e3..6dea6a7 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -5265,8 +5265,98 @@ static struct usb_driver hub_driver = {
>       .supports_autosuspend = 1,
>  };
>  
> +static ssize_t tdrsmdn_show(struct kobject *kobj,
> +             struct kobj_attribute *attr, char *buf)
> +{
> +     return sprintf(buf, "%d\n", usb_timing.tdrsmdn);
> +}
> +
> +static ssize_t tdrsmdn_store(struct kobject *kobj,
> +             struct kobj_attribute *attr, const char *buf, size_t count)
> +{
> +     int ret, val;
> +
> +     ret = kstrtoint(buf, 10, &val);
> +     if (ret < 0)
> +             return ret;
> +
> +     if (val < 20)
> +             usb_timing.tdrsmdn = 20;
> +     else
> +             usb_timing.tdrsmdn = val;

How about:

                usb_timing.rdrsmdn = max(val, USB_TIMING_TDRSMDN_MIN);

and similarly for the others?  And how about making val unsigned?  A 
negative timeout is pretty meaningless.

Alan Stern

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