[U-Boot] [PATCH 2/5] dm: usb: xhci: Implement get_max_xfer_size() operation

[Bin Meng]

xHCD allocates one segment which includes 64 TRBs for each endpoint
and the last TRB in this segment is configured as a link TRB to form
a TRB ring. Each TRB can transfer up to 64K bytes, however data
buffers referenced by transfer TRBs shall not span 64KB boundaries.
Hence the maximum number of TRBs we can use in one transfer is 62.

Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
---

 drivers/usb/host/xhci.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 9b82ee5..04eb1eb 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -1228,6 +1228,20 @@ static int xhci_update_hub_device(struct udevice *dev, struct usb_device *udev)
 	return xhci_configure_endpoints(udev, false);
 }
 
+static int xhci_get_max_xfer_size(struct udevice *dev, size_t *size)
+{
+	/*
+	 * xHCD allocates one segment which includes 64 TRBs for each endpoint
+	 * and the last TRB in this segment is configured as a link TRB to form
+	 * a TRB ring. Each TRB can transfer up to 64K bytes, however data
+	 * buffers referenced by transfer TRBs shall not span 64KB boundaries.
+	 * Hence the maximum number of TRBs we can use in one transfer is 62.
+	 */
+	*size = (TRBS_PER_SEGMENT - 2) * TRB_MAX_BUFF_SIZE;
+
+	return 0;
+}
+
 int xhci_register(struct udevice *dev, struct xhci_hccr *hccr,
 		  struct xhci_hcor *hcor)
 {
@@ -1281,6 +1295,7 @@ struct dm_usb_ops xhci_usb_ops = {
 	.interrupt = xhci_submit_int_msg,
 	.alloc_device = xhci_alloc_device,
 	.update_hub_device = xhci_update_hub_device,
+	.get_max_xfer_size  = xhci_get_max_xfer_size,
 };
 
 #endif
-- 
2.9.2