thunderbolt: Add support for end-to-end flow control

USB4 spec defines end-to-end (E2E) flow control that can be used between
hosts to prevent overflow of a RX ring. We previously had this partially
implemented but that code was removed with commit 53f13319d131
("thunderbolt: Get rid of E2E workaround") with the idea that we add it
back properly if there ever is need. Now that we are going to add DMA
traffic test driver (in subsequent patches) this can be useful.

For this reason we modify tb_ring_alloc_rx/tx() so that they accept
RING_FLAG_E2E and configure the hardware ring accordingly. The RX side
also requires passing TX HopID (e2e_tx_hop) used in the credit grant
packets.

Signed-off-by: Mika Westerberg <[e-mail]>
Acked-by: Yehezkel Bernat <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>

drivers/net/thunderbolt.c

···
 	eof_mask = BIT(TBIP_PDF_FRAME_END);
 
 	ring = tb_ring_alloc_rx(xd->tb->nhi, -1, TBNET_RING_SIZE,
-				RING_FLAG_FRAME, sof_mask, eof_mask,
+				RING_FLAG_FRAME, 0, sof_mask, eof_mask,
 				tbnet_start_poll, net);
 	if (!ring) {
 		netdev_err(dev, "failed to allocate Rx ring\n");

drivers/thunderbolt/ctl.c

···
 	if (!ctl->tx)
 		goto err;
 
-	ctl->rx = tb_ring_alloc_rx(nhi, 0, 10, RING_FLAG_NO_SUSPEND, 0xffff,
-				0xffff, NULL, NULL);
+	ctl->rx = tb_ring_alloc_rx(nhi, 0, 10, RING_FLAG_NO_SUSPEND, 0, 0xffff,
+				   0xffff, NULL, NULL);
 	if (!ctl->rx)
 		goto err;
 

drivers/thunderbolt/nhi.c

···
 
 static struct tb_ring *tb_ring_alloc(struct tb_nhi *nhi, u32 hop, int size,
 				     bool transmit, unsigned int flags,
-				     u16 sof_mask, u16 eof_mask,
+				     int e2e_tx_hop, u16 sof_mask, u16 eof_mask,
 				     void (*start_poll)(void *),
 				     void *poll_data)
 {
···
 	ring->is_tx = transmit;
 	ring->size = size;
 	ring->flags = flags;
+	ring->e2e_tx_hop = e2e_tx_hop;
 	ring->sof_mask = sof_mask;
 	ring->eof_mask = eof_mask;
 	ring->head = 0;
···
 struct tb_ring *tb_ring_alloc_tx(struct tb_nhi *nhi, int hop, int size,
 				 unsigned int flags)
 {
-	return tb_ring_alloc(nhi, hop, size, true, flags, 0, 0, NULL, NULL);
+	return tb_ring_alloc(nhi, hop, size, true, flags, 0, 0, 0, NULL, NULL);
 }
 EXPORT_SYMBOL_GPL(tb_ring_alloc_tx);
 
···
  * @hop: HopID (ring) to allocate. Pass %-1 for automatic allocation.
  * @size: Number of entries in the ring
  * @flags: Flags for the ring
+ * @e2e_tx_hop: Transmit HopID when E2E is enabled in @flags
  * @sof_mask: Mask of PDF values that start a frame
  * @eof_mask: Mask of PDF values that end a frame
  * @start_poll: If not %NULL the ring will call this function when an
···
  * @poll_data: Optional data passed to @start_poll
  */
 struct tb_ring *tb_ring_alloc_rx(struct tb_nhi *nhi, int hop, int size,
-				 unsigned int flags, u16 sof_mask, u16 eof_mask,
+				 unsigned int flags, int e2e_tx_hop,
+				 u16 sof_mask, u16 eof_mask,
 				 void (*start_poll)(void *), void *poll_data)
 {
-	return tb_ring_alloc(nhi, hop, size, false, flags, sof_mask, eof_mask,
+	return tb_ring_alloc(nhi, hop, size, false, flags, e2e_tx_hop, sof_mask, eof_mask,
 			     start_poll, poll_data);
 }
 EXPORT_SYMBOL_GPL(tb_ring_alloc_rx);
···
 		ring_iowrite32options(ring, sof_eof_mask, 4);
 		ring_iowrite32options(ring, flags, 0);
 	}
+
+	/*
+	 * Now that the ring valid bit is set we can configure E2E if
+	 * enabled for the ring.
+	 */
+	if (ring->flags & RING_FLAG_E2E) {
+		if (!ring->is_tx) {
+			u32 hop;
+
+			hop = ring->e2e_tx_hop << REG_RX_OPTIONS_E2E_HOP_SHIFT;
+			hop &= REG_RX_OPTIONS_E2E_HOP_MASK;
+			flags |= hop;
+
+			dev_dbg(&ring->nhi->pdev->dev,
+				"enabling E2E for %s %d with TX HopID %d\n",
+				RING_TYPE(ring), ring->hop, ring->e2e_tx_hop);
+		} else {
+			dev_dbg(&ring->nhi->pdev->dev, "enabling E2E for %s %d\n",
+				RING_TYPE(ring), ring->hop);
+		}
+
+		flags |= RING_FLAG_E2E_FLOW_CONTROL;
+		ring_iowrite32options(ring, flags, 0);
+	}
+
 	ring_interrupt_active(ring, true);
 	ring->running = true;
 err:

include/linux/thunderbolt.h

···
  * @irq: MSI-X irq number if the ring uses MSI-X. %0 otherwise.
  * @vector: MSI-X vector number the ring uses (only set if @irq is > 0)
  * @flags: Ring specific flags
+ * @e2e_tx_hop: Transmit HopID when E2E is enabled. Only applicable to
+ *		RX ring. For TX ring this should be set to %0.
  * @sof_mask: Bit mask used to detect start of frame PDF
  * @eof_mask: Bit mask used to detect end of frame PDF
  * @start_poll: Called when ring interrupt is triggered to start
···
 	int irq;
 	u8 vector;
 	unsigned int flags;
+	int e2e_tx_hop;
 	u16 sof_mask;
 	u16 eof_mask;
 	void (*start_poll)(void *data);
···
 #define RING_FLAG_NO_SUSPEND	BIT(0)
 /* Configure the ring to be in frame mode */
 #define RING_FLAG_FRAME		BIT(1)
+/* Enable end-to-end flow control */
+#define RING_FLAG_E2E		BIT(2)
 
 struct ring_frame;
 typedef void (*ring_cb)(struct tb_ring *, struct ring_frame *, bool canceled);
···
 struct tb_ring *tb_ring_alloc_tx(struct tb_nhi *nhi, int hop, int size,
 				 unsigned int flags);
 struct tb_ring *tb_ring_alloc_rx(struct tb_nhi *nhi, int hop, int size,
-				 unsigned int flags, u16 sof_mask, u16 eof_mask,
+				 unsigned int flags, int e2e_tx_hop,
+				 u16 sof_mask, u16 eof_mask,
 				 void (*start_poll)(void *), void *poll_data);
 void tb_ring_start(struct tb_ring *ring);
 void tb_ring_stop(struct tb_ring *ring);