From: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> commit 1bf2761c837571a66ec290fb66c90413821ffda2 upstream. Maximum Exit Latency (MEL) value is used by host to know how much in advance it needs to start waking up a U1/U2 suspended link in order to service a periodic transfer in time. Current MEL calculation only includes the time to wake up the path from U1/U2 to U0. This is called tMEL1 in USB 3.1 section C 1.5.2 Total MEL = tMEL1 + tMEL2 +tMEL3 + tMEL4 which should additinally include: - tMEL2 which is the time it takes for PING message to reach device - tMEL3 time for device to process the PING and submit a PING_RESPONSE - tMEL4 time for PING_RESPONSE to traverse back upstream to host. Add the missing tMEL2, tMEL3 and tMEL4 to MEL calculation. Cc: <stable@xxxxxxxxxx> # v3.5 Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210715150122.1995966-1-mathias.nyman@xxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/usb/core/hub.c | 52 ++++++++++++++++++++++++++----------------------- 1 file changed, 28 insertions(+), 24 deletions(-) --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -47,6 +47,7 @@ #define USB_TP_TRANSMISSION_DELAY 40 /* ns */ #define USB_TP_TRANSMISSION_DELAY_MAX 65535 /* ns */ +#define USB_PING_RESPONSE_TIME 400 /* ns */ /* Protect struct usb_device->state and ->children members * Note: Both are also protected by ->dev.sem, except that ->state can @@ -181,8 +182,9 @@ int usb_device_supports_lpm(struct usb_d } /* - * Set the Maximum Exit Latency (MEL) for the host to initiate a transition from - * either U1 or U2. + * Set the Maximum Exit Latency (MEL) for the host to wakup up the path from + * U1/U2, send a PING to the device and receive a PING_RESPONSE. + * See USB 3.1 section C.1.5.2 */ static void usb_set_lpm_mel(struct usb_device *udev, struct usb3_lpm_parameters *udev_lpm_params, @@ -192,35 +194,37 @@ static void usb_set_lpm_mel(struct usb_d unsigned int hub_exit_latency) { unsigned int total_mel; - unsigned int device_mel; - unsigned int hub_mel; /* - * Calculate the time it takes to transition all links from the roothub - * to the parent hub into U0. The parent hub must then decode the - * packet (hub header decode latency) to figure out which port it was - * bound for. - * - * The Hub Header decode latency is expressed in 0.1us intervals (0x1 - * means 0.1us). Multiply that by 100 to get nanoseconds. + * tMEL1. time to transition path from host to device into U0. + * MEL for parent already contains the delay up to parent, so only add + * the exit latency for the last link (pick the slower exit latency), + * and the hub header decode latency. See USB 3.1 section C 2.2.1 + * Store MEL in nanoseconds */ total_mel = hub_lpm_params->mel + - (hub->descriptor->u.ss.bHubHdrDecLat * 100); + max(udev_exit_latency, hub_exit_latency) * 1000 + + hub->descriptor->u.ss.bHubHdrDecLat * 100; /* - * How long will it take to transition the downstream hub's port into - * U0? The greater of either the hub exit latency or the device exit - * latency. - * - * The BOS U1/U2 exit latencies are expressed in 1us intervals. - * Multiply that by 1000 to get nanoseconds. + * tMEL2. Time to submit PING packet. Sum of tTPTransmissionDelay for + * each link + wHubDelay for each hub. Add only for last link. + * tMEL4, the time for PING_RESPONSE to traverse upstream is similar. + * Multiply by 2 to include it as well. */ - device_mel = udev_exit_latency * 1000; - hub_mel = hub_exit_latency * 1000; - if (device_mel > hub_mel) - total_mel += device_mel; - else - total_mel += hub_mel; + total_mel += (__le16_to_cpu(hub->descriptor->u.ss.wHubDelay) + + USB_TP_TRANSMISSION_DELAY) * 2; + + /* + * tMEL3, tPingResponse. Time taken by device to generate PING_RESPONSE + * after receiving PING. Also add 2100ns as stated in USB 3.1 C 1.5.2.4 + * to cover the delay if the PING_RESPONSE is queued behind a Max Packet + * Size DP. + * Note these delays should be added only once for the entire path, so + * add them to the MEL of the device connected to the roothub. + */ + if (!hub->hdev->parent) + total_mel += USB_PING_RESPONSE_TIME + 2100; udev_lpm_params->mel = total_mel; }
