On 10.4.2021 3.47, Thinh Nguyen wrote:
> DWC_usb31 host version 1.90a and prior undercalculates the bandwidth
> available for interrupt endpoints. The controller will return bandwidth
> error on config endpoint commands if there are already 6 or more
> fullspeed interrupt endpoints with bInterval of 4 (or 4ms) associated
> with a single fullspeed bus instance (BI).
>
> To workaround this, configure and use the endpoint at a shorter
> interrupt interval. Lower the ep_ctx interval from 5 to 4 (or 2ms)
> for interrupt endpoints of the fullspeed BI. Note: we have not observed
> functional impact to the fullspeed devices by lowering the interrupt
> service interval (at least for a few devices that we tested).
>
> To simplify the workaround, let's just check and apply the workaround if
> the endpoint is a fullspeed interrupt endpoint with interval of 4ms and
> if the top parent device is also operating in fullspeed (i.e. associated
> with fullspeed BI).
>
> Signed-off-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
> ---
> Changes in v2:
> - None
>
> Note:
> Checkpatch will give a warning below for getting top_dev:
> WARNING: suspect code indent for conditional statements
>
> Since this logic is done everywhere else in the driver, I'm keeping it
> consistent here.
>
> drivers/usb/host/xhci-mem.c | 23 +++++++++++++++++++++++
> include/linux/usb/xhci-quirks.h | 1 +
> 2 files changed, 24 insertions(+)
>
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 1053b43008e4..e01d0ddb012a 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -1463,6 +1463,29 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
> }
> }
>
> + /*
> + * Check for undercalculated bandwidth quirk for interrupt endpoints
> + * associated with fullspeed BI.
> + */
> + if ((xhci->quirks & XHCI_LIMIT_FS_BI_INTR_EP) &&
> + usb_endpoint_xfer_int(&ep->desc) &&
> + udev->speed == USB_SPEED_FULL &&
> + interval == 5) {
> + struct usb_device *top_dev;
> +
> + for (top_dev = udev;
> + top_dev->parent && top_dev->parent->parent;
> + top_dev = top_dev->parent)
> + /* Found device below root hub */;
> +
> + /*
> + * If the top device is operating at fullspeed, then the
> + * controller is using fullspeed BI for this device.
> + */
> + if (top_dev->speed == USB_SPEED_FULL)
> + interval = 4;
> + }
> +
If we write a new xhci-snps driver then adjusting the interval could be done in the
.add_endpoint override, after calling xhci_add_endpoint()
If not then something like this should work.
Maybe turn it into a separate function for readability.
xhci_tune_interval_quirk(xhci, udev, ep, &interval)
-Mathias
