Save 80ms device enumeration time by increasing root hub port reset time The 50ms reset signaling time is not enough for most root hub ports. Increasing the reset time to 60ms allows host controllers to finish port reset and removes a retry causing an extra 50ms delay. The USB 2 specification requires "at least 50ms" for driving root port reset. The current msleep is exactly 50ms which may not be enough if there are any delays between writing the reset bit to host controller portsc register and phy actually driving reset. On Haswell, Skylake and Kabylake xHC port reset took in average 52-59ms The 80ms improvement comes from (40ms * 2 port resets) save at enumeration for each device connected to a root hub port. more details about root port reset in USB2 section 7.1.7.5:. "Software must ensure that resets issued to the root ports drive reset long enough to overwhelm any concurrent resume attempts by downstream devices. It is required that resets from root ports have a duration of at least 50 ms (TDRSTR). Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> --- drivers/usb/core/hub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index e53308c..41eaf0b 100644 --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -2614,7 +2614,7 @@ static unsigned hub_is_wusb(struct usb_hub *hub) #define SET_CONFIG_TRIES (2 * (use_both_schemes + 1)) #define USE_NEW_SCHEME(i) ((i) / 2 == (int)old_scheme_first) -#define HUB_ROOT_RESET_TIME 50 /* times are in msec */ +#define HUB_ROOT_RESET_TIME 60 /* times are in msec */ #define HUB_SHORT_RESET_TIME 10 #define HUB_BH_RESET_TIME 50 #define HUB_LONG_RESET_TIME 200 -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
