usb: dwc3: gadget: Handle stream transfers

Overview of stream transfer requirement:
 * A transfer will have a set of TRBs of the same stream ID.
 * A transfer is started with a stream ID in START_TRANSFER command.
 * A new stream will only start when the previous completes.

Overview of stream events:
 * A "prime" from host indicates that its endpoints are active
   (buffers prepared and ready to receive/transmit data). The controller
   automatically initiates stream if it sees this.
 * A "NoStream" rejection event indicates that the host isn't ready.
   Host will put the endpoint back to idle state. Device may need to
   reinitiate the stream to start transfer again.
 * A Stream Found event means host accepted device initiated stream.
   Nothing needs to be done from driver.

To initiate a stream, the driver will issue START_TRANSFER command with
a stream ID. To reinitiate the stream, the driver must issue
END_TRANSFER and restart the transfer with START_TRANSFER command with
the same stream ID.

This implementation handles device-initated streams (e.g. UASP driver).
It also handles some hosts' quirky behavior where they only prime each
endpoint once.

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/usb/dwc3/debug.h b/drivers/usb/dwc3/debug.h
index 0f95656c9622..d8f600e0e88f 100644
--- a/drivers/usb/dwc3/debug.h
+++ b/drivers/usb/dwc3/debug.h
@@ -68,6 +68,8 @@ dwc3_gadget_generic_cmd_string(u8 cmd)
 		return "All FIFO Flush";
 	case DWC3_DGCMD_SET_ENDPOINT_NRDY:
 		return "Set Endpoint NRDY";
+	case DWC3_DGCMD_SET_ENDPOINT_PRIME:
+		return "Set Endpoint Prime";
 	case DWC3_DGCMD_RUN_SOC_BUS_LOOPBACK:
 		return "Run SoC Bus Loopback Test";
 	default: