gve: move DQO rx buffer management related code to a new file

In preparation for the upcoming page pool adoption for DQO
raw addressing mode, move RX buffer management code to a new
file. In the follow on patches, page pool code will be added
to this file.

No functional change, just movement of code.

Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Shailend Chand <shailend@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20241014202108.1051963-2-pkaligineedi@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/google/gve/Makefile

@@ -1,4 +1,5 @@
 # Makefile for the Google virtual Ethernet (gve) driver
 
 obj-$(CONFIG_GVE) += gve.o
-gve-objs := gve_main.o gve_tx.o gve_tx_dqo.o gve_rx.o gve_rx_dqo.o gve_ethtool.o gve_adminq.o gve_utils.o gve_flow_rule.o
+gve-objs := gve_main.o gve_tx.o gve_tx_dqo.o gve_rx.o gve_rx_dqo.o gve_ethtool.o gve_adminq.o gve_utils.o gve_flow_rule.o \
+	    gve_buffer_mgmt_dqo.o

drivers/net/ethernet/google/gve/gve.h

@@ -1162,6 +1162,24 @@ void gve_rx_stop_ring_gqi(struct gve_priv *priv, int idx);
 u16 gve_get_pkt_buf_size(const struct gve_priv *priv, bool enable_hplit);
 bool gve_header_split_supported(const struct gve_priv *priv);
 int gve_set_hsplit_config(struct gve_priv *priv, u8 tcp_data_split);
+/* rx buffer handling */
+int gve_buf_ref_cnt(struct gve_rx_buf_state_dqo *bs);
+void gve_free_page_dqo(struct gve_priv *priv, struct gve_rx_buf_state_dqo *bs,
+		       bool free_page);
+struct gve_rx_buf_state_dqo *gve_alloc_buf_state(struct gve_rx_ring *rx);
+bool gve_buf_state_is_allocated(struct gve_rx_ring *rx,
+				struct gve_rx_buf_state_dqo *buf_state);
+void gve_free_buf_state(struct gve_rx_ring *rx,
+			struct gve_rx_buf_state_dqo *buf_state);
+struct gve_rx_buf_state_dqo *gve_dequeue_buf_state(struct gve_rx_ring *rx,
+						   struct gve_index_list *list);
+void gve_enqueue_buf_state(struct gve_rx_ring *rx, struct gve_index_list *list,
+			   struct gve_rx_buf_state_dqo *buf_state);
+struct gve_rx_buf_state_dqo *gve_get_recycled_buf_state(struct gve_rx_ring *rx);
+int gve_alloc_page_dqo(struct gve_rx_ring *rx,
+		       struct gve_rx_buf_state_dqo *buf_state);
+void gve_try_recycle_buf(struct gve_priv *priv, struct gve_rx_ring *rx,
+			 struct gve_rx_buf_state_dqo *buf_state);
 /* Reset */
 void gve_schedule_reset(struct gve_priv *priv);
 int gve_reset(struct gve_priv *priv, bool attempt_teardown);

drivers/net/ethernet/google/gve/gve_buffer_mgmt_dqo.c

@@ -0,0 +1,230 @@
+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+/* Google virtual Ethernet (gve) driver
+ *
+ * Copyright (C) 2015-2024 Google, Inc.
+ */
+
+#include "gve.h"
+#include "gve_utils.h"
+
+int gve_buf_ref_cnt(struct gve_rx_buf_state_dqo *bs)
+{
+	return page_count(bs->page_info.page) - bs->page_info.pagecnt_bias;
+}
+
+void gve_free_page_dqo(struct gve_priv *priv, struct gve_rx_buf_state_dqo *bs,
+		       bool free_page)
+{
+	page_ref_sub(bs->page_info.page, bs->page_info.pagecnt_bias - 1);
+	if (free_page)
+		gve_free_page(&priv->pdev->dev, bs->page_info.page, bs->addr,
+			      DMA_FROM_DEVICE);
+	bs->page_info.page = NULL;
+}
+
+struct gve_rx_buf_state_dqo *gve_alloc_buf_state(struct gve_rx_ring *rx)
+{
+	struct gve_rx_buf_state_dqo *buf_state;
+	s16 buffer_id;
+
+	buffer_id = rx->dqo.free_buf_states;
+	if (unlikely(buffer_id == -1))
+		return NULL;
+
+	buf_state = &rx->dqo.buf_states[buffer_id];
+
+	/* Remove buf_state from free list */
+	rx->dqo.free_buf_states = buf_state->next;
+
+	/* Point buf_state to itself to mark it as allocated */
+	buf_state->next = buffer_id;
+
+	return buf_state;
+}
+
+bool gve_buf_state_is_allocated(struct gve_rx_ring *rx,
+				struct gve_rx_buf_state_dqo *buf_state)
+{
+	s16 buffer_id = buf_state - rx->dqo.buf_states;
+
+	return buf_state->next == buffer_id;
+}
+
+void gve_free_buf_state(struct gve_rx_ring *rx,
+			struct gve_rx_buf_state_dqo *buf_state)
+{
+	s16 buffer_id = buf_state - rx->dqo.buf_states;
+
+	buf_state->next = rx->dqo.free_buf_states;
+	rx->dqo.free_buf_states = buffer_id;
+}
+
+struct gve_rx_buf_state_dqo *gve_dequeue_buf_state(struct gve_rx_ring *rx,
+						   struct gve_index_list *list)
+{
+	struct gve_rx_buf_state_dqo *buf_state;
+	s16 buffer_id;
+
+	buffer_id = list->head;
+	if (unlikely(buffer_id == -1))
+		return NULL;
+
+	buf_state = &rx->dqo.buf_states[buffer_id];
+
+	/* Remove buf_state from list */
+	list->head = buf_state->next;
+	if (buf_state->next == -1)
+		list->tail = -1;
+
+	/* Point buf_state to itself to mark it as allocated */
+	buf_state->next = buffer_id;
+
+	return buf_state;
+}
+
+void gve_enqueue_buf_state(struct gve_rx_ring *rx, struct gve_index_list *list,
+			   struct gve_rx_buf_state_dqo *buf_state)
+{
+	s16 buffer_id = buf_state - rx->dqo.buf_states;
+
+	buf_state->next = -1;
+
+	if (list->head == -1) {
+		list->head = buffer_id;
+		list->tail = buffer_id;
+	} else {
+		int tail = list->tail;
+
+		rx->dqo.buf_states[tail].next = buffer_id;
+		list->tail = buffer_id;
+	}
+}
+
+struct gve_rx_buf_state_dqo *gve_get_recycled_buf_state(struct gve_rx_ring *rx)
+{
+	struct gve_rx_buf_state_dqo *buf_state;
+	int i;
+
+	/* Recycled buf states are immediately usable. */
+	buf_state = gve_dequeue_buf_state(rx, &rx->dqo.recycled_buf_states);
+	if (likely(buf_state))
+		return buf_state;
+
+	if (unlikely(rx->dqo.used_buf_states.head == -1))
+		return NULL;
+
+	/* Used buf states are only usable when ref count reaches 0, which means
+	 * no SKBs refer to them.
+	 *
+	 * Search a limited number before giving up.
+	 */
+	for (i = 0; i < 5; i++) {
+		buf_state = gve_dequeue_buf_state(rx, &rx->dqo.used_buf_states);
+		if (gve_buf_ref_cnt(buf_state) == 0) {
+			rx->dqo.used_buf_states_cnt--;
+			return buf_state;
+		}
+
+		gve_enqueue_buf_state(rx, &rx->dqo.used_buf_states, buf_state);
+	}
+
+	/* For QPL, we cannot allocate any new buffers and must
+	 * wait for the existing ones to be available.
+	 */
+	if (rx->dqo.qpl)
+		return NULL;
+
+	/* If there are no free buf states discard an entry from
+	 * `used_buf_states` so it can be used.
+	 */
+	if (unlikely(rx->dqo.free_buf_states == -1)) {
+		buf_state = gve_dequeue_buf_state(rx, &rx->dqo.used_buf_states);
+		if (gve_buf_ref_cnt(buf_state) == 0)
+			return buf_state;
+
+		gve_free_page_dqo(rx->gve, buf_state, true);
+		gve_free_buf_state(rx, buf_state);
+	}
+
+	return NULL;
+}
+
+int gve_alloc_page_dqo(struct gve_rx_ring *rx,
+		       struct gve_rx_buf_state_dqo *buf_state)
+{
+	struct gve_priv *priv = rx->gve;
+	u32 idx;
+
+	if (!rx->dqo.qpl) {
+		int err;
+
+		err = gve_alloc_page(priv, &priv->pdev->dev,
+				     &buf_state->page_info.page,
+				     &buf_state->addr,
+				     DMA_FROM_DEVICE, GFP_ATOMIC);
+		if (err)
+			return err;
+	} else {
+		idx = rx->dqo.next_qpl_page_idx;
+		if (idx >= gve_get_rx_pages_per_qpl_dqo(priv->rx_desc_cnt)) {
+			net_err_ratelimited("%s: Out of QPL pages\n",
+					    priv->dev->name);
+			return -ENOMEM;
+		}
+		buf_state->page_info.page = rx->dqo.qpl->pages[idx];
+		buf_state->addr = rx->dqo.qpl->page_buses[idx];
+		rx->dqo.next_qpl_page_idx++;
+	}
+	buf_state->page_info.page_offset = 0;
+	buf_state->page_info.page_address =
+		page_address(buf_state->page_info.page);
+	buf_state->last_single_ref_offset = 0;
+
+	/* The page already has 1 ref. */
+	page_ref_add(buf_state->page_info.page, INT_MAX - 1);
+	buf_state->page_info.pagecnt_bias = INT_MAX;
+
+	return 0;
+}
+
+void gve_try_recycle_buf(struct gve_priv *priv, struct gve_rx_ring *rx,
+			 struct gve_rx_buf_state_dqo *buf_state)
+{
+	const u16 data_buffer_size = priv->data_buffer_size_dqo;
+	int pagecount;
+
+	/* Can't reuse if we only fit one buffer per page */
+	if (data_buffer_size * 2 > PAGE_SIZE)
+		goto mark_used;
+
+	pagecount = gve_buf_ref_cnt(buf_state);
+
+	/* Record the offset when we have a single remaining reference.
+	 *
+	 * When this happens, we know all of the other offsets of the page are
+	 * usable.
+	 */
+	if (pagecount == 1) {
+		buf_state->last_single_ref_offset =
+			buf_state->page_info.page_offset;
+	}
+
+	/* Use the next buffer sized chunk in the page. */
+	buf_state->page_info.page_offset += data_buffer_size;
+	buf_state->page_info.page_offset &= (PAGE_SIZE - 1);
+
+	/* If we wrap around to the same offset without ever dropping to 1
+	 * reference, then we don't know if this offset was ever freed.
+	 */
+	if (buf_state->page_info.page_offset ==
+	    buf_state->last_single_ref_offset) {
+		goto mark_used;
+	}
+
+	gve_enqueue_buf_state(rx, &rx->dqo.recycled_buf_states, buf_state);
+	return;
+
+mark_used:
+	gve_enqueue_buf_state(rx, &rx->dqo.used_buf_states, buf_state);
+	rx->dqo.used_buf_states_cnt++;
+}