[PATCH net-next v4 2/2] net: dsa: yt921x: Use u64_stats_t for MIB stats

David Yang
2026-01-08T00:43:30Z

64-bit variables might not be atomic on 32-bit architectures, thus
cannot be unconditionally made lock-free. Use u64_stats_t so it would
still be lock-free on 64-bit architectures.

Signed-off-by: David Yang <mmyangfl@gmail.com>
---
drivers/net/dsa/yt921x.c | 244 +++++++++++++++++++++++----------------
drivers/net/dsa/yt921x.h | 108 +++++++++--------
2 files changed, 204 insertions(+), 148 deletions(-)

diff --git a/drivers/net/dsa/yt921x.c b/drivers/net/dsa/yt921x.c
index 5e4e8093ba16..eee6652cee39 100644
--- a/drivers/net/dsa/yt921x.c
+++ b/drivers/net/dsa/yt921x.c
@@ -18,6 +18,7 @@
#include <linux/of.h>
#include <linux/of_mdio.h>
#include <linux/of_net.h>
+#include <linux/u64_stats_sync.h>

#include <net/dsa.h>

@@ -666,22 +667,20 @@ yt921x_mbus_ext_init(struct yt921x_priv *priv, struct device_node *mnp)
static int yt921x_read_mib(struct yt921x_priv *priv, int port)
{
struct yt921x_port *pp = &priv->ports[port];
+ struct yt921x_mib *mib_new = &pp->mib_new;
struct device *dev = to_device(priv);
struct yt921x_mib *mib = &pp->mib;
+ u64 rx_frames;
+ u64 tx_frames;
int res = 0;

- /* Reading of yt921x_port::mib is not protected by a lock and it's vain
- * to keep its consistency, since we have to read registers one by one
- * and there is no way to make a snapshot of MIB stats.
- *
- * Writing (by this function only) is and should be protected by
- * reg_lock.
+ /* u64_stats_read/set is redundant for mib_new, but I don't want to
+ * declare a plain u64 yt921x_mib variant.
*/

for (size_t i = 0; i < ARRAY_SIZE(yt921x_mib_descs); i++) {
const struct yt921x_mib_desc *desc = &yt921x_mib_descs[i];
u32 reg = YT921X_MIBn_DATA0(port) + desc->offset;
- u64 *valp = &((u64 *)mib)[i];
u32 val0;
u64 val;

@@ -690,7 +689,7 @@ static int yt921x_read_mib(struct yt921x_priv *priv, int port)
break;

if (desc->size <= 1) {
- u64 old_val = *valp;
+ u64 old_val = u64_stats_read(&((u64_stats_t *)mib)[i]);

val = (old_val & ~(u64)U32_MAX) | val0;
if (val < old_val)
@@ -704,22 +703,40 @@ static int yt921x_read_mib(struct yt921x_priv *priv, int port)
val = ((u64)val1 << 32) | val0;
}

- WRITE_ONCE(*valp, val);
+ u64_stats_set(&((u64_stats_t *)mib_new)[i], val);
}

- pp->rx_frames = mib->rx_64byte + mib->rx_65_127byte +
- mib->rx_128_255byte + mib->rx_256_511byte +
- mib->rx_512_1023byte + mib->rx_1024_1518byte +
- mib->rx_jumbo;
- pp->tx_frames = mib->tx_64byte + mib->tx_65_127byte +
- mib->tx_128_255byte + mib->tx_256_511byte +
- mib->tx_512_1023byte + mib->tx_1024_1518byte +
- mib->tx_jumbo;
-
- if (res)
+ if (res) {
dev_err(dev, "Failed to %s port %d: %i\n", "read stats for",
port, res);
- return res;
+ return res;
+ }
+
+ rx_frames = u64_stats_read(&mib_new->rx_64byte) +
+ u64_stats_read(&mib_new->rx_65_127byte) +
+ u64_stats_read(&mib_new->rx_128_255byte) +
+ u64_stats_read(&mib_new->rx_256_511byte) +
+ u64_stats_read(&mib_new->rx_512_1023byte) +
+ u64_stats_read(&mib_new->rx_1024_1518byte) +
+ u64_stats_read(&mib_new->rx_jumbo);
+ tx_frames = u64_stats_read(&mib_new->tx_64byte) +
+ u64_stats_read(&mib_new->tx_65_127byte) +
+ u64_stats_read(&mib_new->tx_128_255byte) +
+ u64_stats_read(&mib_new->tx_256_511byte) +
+ u64_stats_read(&mib_new->tx_512_1023byte) +
+ u64_stats_read(&mib_new->tx_1024_1518byte) +
+ u64_stats_read(&mib_new->tx_jumbo);
+
+ u64_stats_update_begin(&pp->syncp);
+ for (size_t i = 0; i < ARRAY_SIZE(yt921x_mib_descs); i++) {
+ u64_stats_set(&((u64_stats_t *)mib)[i],
+ u64_stats_read(&((u64_stats_t *)mib_new)[i]));
+ }
+ u64_stats_set(&pp->rx_frames, rx_frames);
+ u64_stats_set(&pp->tx_frames, tx_frames);
+ u64_stats_update_end(&pp->syncp);
+
+ return 0;
}

static void yt921x_poll_mib(struct work_struct *work)
@@ -762,22 +779,27 @@ yt921x_dsa_get_ethtool_stats(struct dsa_switch *ds, int port, uint64_t *data)
struct yt921x_priv *priv = to_yt921x_priv(ds);
struct yt921x_port *pp = &priv->ports[port];
struct yt921x_mib *mib = &pp->mib;
+ unsigned int start;
size_t j;

mutex_lock(&priv->reg_lock);
yt921x_read_mib(priv, port);
mutex_unlock(&priv->reg_lock);

- j = 0;
- for (size_t i = 0; i < ARRAY_SIZE(yt921x_mib_descs); i++) {
- const struct yt921x_mib_desc *desc = &yt921x_mib_descs[i];
+ do {
+ start = u64_stats_fetch_begin(&pp->syncp);

- if (!desc->name)
- continue;
+ j = 0;
+ for (size_t i = 0; i < ARRAY_SIZE(yt921x_mib_descs); i++) {
+ const struct yt921x_mib_desc *desc = &yt921x_mib_descs[i];

- data[j] = ((u64 *)mib)[i];
- j++;
- }
+ if (!desc->name)
+ continue;
+
+ data[j] = u64_stats_read(&((u64_stats_t *)mib)[i]);
+ j++;
+ }
+ } while (u64_stats_fetch_retry(&pp->syncp, start));
}

static int yt921x_dsa_get_sset_count(struct dsa_switch *ds, int port, int sset)
@@ -804,33 +826,38 @@ yt921x_dsa_get_eth_mac_stats(struct dsa_switch *ds, int port,
struct yt921x_priv *priv = to_yt921x_priv(ds);
struct yt921x_port *pp = &priv->ports[port];
struct yt921x_mib *mib = &pp->mib;
+ unsigned int start;

mutex_lock(&priv->reg_lock);
yt921x_read_mib(priv, port);
mutex_unlock(&priv->reg_lock);

- mac_stats->FramesTransmittedOK = pp->tx_frames;
- mac_stats->SingleCollisionFrames = mib->tx_single_collisions;
- mac_stats->MultipleCollisionFrames = mib->tx_multiple_collisions;
- mac_stats->FramesReceivedOK = pp->rx_frames;
- mac_stats->FrameCheckSequenceErrors = mib->rx_crc_errors;
- mac_stats->AlignmentErrors = mib->rx_alignment_errors;
- mac_stats->OctetsTransmittedOK = mib->tx_good_bytes;
- mac_stats->FramesWithDeferredXmissions = mib->tx_deferred;
- mac_stats->LateCollisions = mib->tx_late_collisions;
- mac_stats->FramesAbortedDueToXSColls = mib->tx_aborted_errors;
- /* mac_stats->FramesLostDueToIntMACXmitError */
- /* mac_stats->CarrierSenseErrors */
- mac_stats->OctetsReceivedOK = mib->rx_good_bytes;
- /* mac_stats->FramesLostDueToIntMACRcvError */
- mac_stats->MulticastFramesXmittedOK = mib->tx_multicast;
- mac_stats->BroadcastFramesXmittedOK = mib->tx_broadcast;
- /* mac_stats->FramesWithExcessiveDeferral */
- mac_stats->MulticastFramesReceivedOK = mib->rx_multicast;
- mac_stats->BroadcastFramesReceivedOK = mib->rx_broadcast;
- /* mac_stats->InRangeLengthErrors */
- /* mac_stats->OutOfRangeLengthField */
- mac_stats->FrameTooLongErrors = mib->rx_oversize_errors;
+ do {
+ start = u64_stats_fetch_begin(&pp->syncp);
+
+ mac_stats->FramesTransmittedOK = u64_stats_read(&pp->tx_frames);
+ mac_stats->SingleCollisionFrames = u64_stats_read(&mib->tx_single_collisions);
+ mac_stats->MultipleCollisionFrames = u64_stats_read(&mib->tx_multiple_collisions);
+ mac_stats->FramesReceivedOK = u64_stats_read(&pp->rx_frames);
+ mac_stats->FrameCheckSequenceErrors = u64_stats_read(&mib->rx_crc_errors);
+ mac_stats->AlignmentErrors = u64_stats_read(&mib->rx_alignment_errors);
+ mac_stats->OctetsTransmittedOK = u64_stats_read(&mib->tx_good_bytes);
+ mac_stats->FramesWithDeferredXmissions = u64_stats_read(&mib->tx_deferred);
+ mac_stats->LateCollisions = u64_stats_read(&mib->tx_late_collisions);
+ mac_stats->FramesAbortedDueToXSColls = u64_stats_read(&mib->tx_aborted_errors);
+ /* mac_stats->FramesLostDueToIntMACXmitError */
+ /* mac_stats->CarrierSenseErrors */
+ mac_stats->OctetsReceivedOK = u64_stats_read(&mib->rx_good_bytes);
+ /* mac_stats->FramesLostDueToIntMACRcvError */
+ mac_stats->MulticastFramesXmittedOK = u64_stats_read(&mib->tx_multicast);
+ mac_stats->BroadcastFramesXmittedOK = u64_stats_read(&mib->tx_broadcast);
+ /* mac_stats->FramesWithExcessiveDeferral */
+ mac_stats->MulticastFramesReceivedOK = u64_stats_read(&mib->rx_multicast);
+ mac_stats->BroadcastFramesReceivedOK = u64_stats_read(&mib->rx_broadcast);
+ /* mac_stats->InRangeLengthErrors */
+ /* mac_stats->OutOfRangeLengthField */
+ mac_stats->FrameTooLongErrors = u64_stats_read(&mib->rx_oversize_errors);
+ } while (u64_stats_fetch_retry(&pp->syncp, start));
}

static void
@@ -840,14 +867,19 @@ yt921x_dsa_get_eth_ctrl_stats(struct dsa_switch *ds, int port,
struct yt921x_priv *priv = to_yt921x_priv(ds);
struct yt921x_port *pp = &priv->ports[port];
struct yt921x_mib *mib = &pp->mib;
+ unsigned int start;

mutex_lock(&priv->reg_lock);
yt921x_read_mib(priv, port);
mutex_unlock(&priv->reg_lock);

- ctrl_stats->MACControlFramesTransmitted = mib->tx_pause;
- ctrl_stats->MACControlFramesReceived = mib->rx_pause;
- /* ctrl_stats->UnsupportedOpcodesReceived */
+ do {
+ start = u64_stats_fetch_begin(&pp->syncp);
+
+ ctrl_stats->MACControlFramesTransmitted = u64_stats_read(&mib->tx_pause);
+ ctrl_stats->MACControlFramesReceived = u64_stats_read(&mib->rx_pause);
+ /* ctrl_stats->UnsupportedOpcodesReceived */
+ } while (u64_stats_fetch_retry(&pp->syncp, start));
}

static const struct ethtool_rmon_hist_range yt921x_rmon_ranges[] = {
@@ -869,6 +901,7 @@ yt921x_dsa_get_rmon_stats(struct dsa_switch *ds, int port,
struct yt921x_priv *priv = to_yt921x_priv(ds);
struct yt921x_port *pp = &priv->ports[port];
struct yt921x_mib *mib = &pp->mib;
+ unsigned int start;

mutex_lock(&priv->reg_lock);
yt921x_read_mib(priv, port);
@@ -876,26 +909,30 @@ yt921x_dsa_get_rmon_stats(struct dsa_switch *ds, int port,

*ranges = yt921x_rmon_ranges;

- rmon_stats->undersize_pkts = mib->rx_undersize_errors;
- rmon_stats->oversize_pkts = mib->rx_oversize_errors;
- rmon_stats->fragments = mib->rx_alignment_errors;
- /* rmon_stats->jabbers */
-
- rmon_stats->hist[0] = mib->rx_64byte;
- rmon_stats->hist[1] = mib->rx_65_127byte;
- rmon_stats->hist[2] = mib->rx_128_255byte;
- rmon_stats->hist[3] = mib->rx_256_511byte;
- rmon_stats->hist[4] = mib->rx_512_1023byte;
- rmon_stats->hist[5] = mib->rx_1024_1518byte;
- rmon_stats->hist[6] = mib->rx_jumbo;
-
- rmon_stats->hist_tx[0] = mib->tx_64byte;
- rmon_stats->hist_tx[1] = mib->tx_65_127byte;
- rmon_stats->hist_tx[2] = mib->tx_128_255byte;
- rmon_stats->hist_tx[3] = mib->tx_256_511byte;
- rmon_stats->hist_tx[4] = mib->tx_512_1023byte;
- rmon_stats->hist_tx[5] = mib->tx_1024_1518byte;
- rmon_stats->hist_tx[6] = mib->tx_jumbo;
+ do {
+ start = u64_stats_fetch_begin(&pp->syncp);
+
+ rmon_stats->undersize_pkts = u64_stats_read(&mib->rx_undersize_errors);
+ rmon_stats->oversize_pkts = u64_stats_read(&mib->rx_oversize_errors);
+ rmon_stats->fragments = u64_stats_read(&mib->rx_alignment_errors);
+ /* rmon_stats->jabbers */
+
+ rmon_stats->hist[0] = u64_stats_read(&mib->rx_64byte);
+ rmon_stats->hist[1] = u64_stats_read(&mib->rx_65_127byte);
+ rmon_stats->hist[2] = u64_stats_read(&mib->rx_128_255byte);
+ rmon_stats->hist[3] = u64_stats_read(&mib->rx_256_511byte);
+ rmon_stats->hist[4] = u64_stats_read(&mib->rx_512_1023byte);
+ rmon_stats->hist[5] = u64_stats_read(&mib->rx_1024_1518byte);
+ rmon_stats->hist[6] = u64_stats_read(&mib->rx_jumbo);
+
+ rmon_stats->hist_tx[0] = u64_stats_read(&mib->tx_64byte);
+ rmon_stats->hist_tx[1] = u64_stats_read(&mib->tx_65_127byte);
+ rmon_stats->hist_tx[2] = u64_stats_read(&mib->tx_128_255byte);
+ rmon_stats->hist_tx[3] = u64_stats_read(&mib->tx_256_511byte);
+ rmon_stats->hist_tx[4] = u64_stats_read(&mib->tx_512_1023byte);
+ rmon_stats->hist_tx[5] = u64_stats_read(&mib->tx_1024_1518byte);
+ rmon_stats->hist_tx[6] = u64_stats_read(&mib->tx_jumbo);
+ } while (u64_stats_fetch_retry(&pp->syncp, start));
}

static void
@@ -905,33 +942,41 @@ yt921x_dsa_get_stats64(struct dsa_switch *ds, int port,
struct yt921x_priv *priv = to_yt921x_priv(ds);
struct yt921x_port *pp = &priv->ports[port];
struct yt921x_mib *mib = &pp->mib;
+ unsigned int start;
+
+ do {
+ start = u64_stats_fetch_begin(&pp->syncp);
+
+ stats->rx_length_errors = u64_stats_read(&mib->rx_undersize_errors) +
+ u64_stats_read(&mib->rx_fragment_errors);
+ stats->rx_over_errors = u64_stats_read(&mib->rx_oversize_errors);
+ stats->rx_crc_errors = u64_stats_read(&mib->rx_crc_errors);
+ stats->rx_frame_errors = u64_stats_read(&mib->rx_alignment_errors);
+ /* stats->rx_fifo_errors */
+ /* stats->rx_missed_errors */
+
+ stats->tx_aborted_errors = u64_stats_read(&mib->tx_aborted_errors);
+ /* stats->tx_carrier_errors */
+ stats->tx_fifo_errors = u64_stats_read(&mib->tx_undersize_errors);
+ /* stats->tx_heartbeat_errors */
+ stats->tx_window_errors = u64_stats_read(&mib->tx_late_collisions);
+
+ stats->rx_packets = u64_stats_read(&pp->rx_frames);
+ stats->tx_packets = u64_stats_read(&pp->tx_frames);
+ stats->rx_bytes = u64_stats_read(&mib->rx_good_bytes) -
+ ETH_FCS_LEN * stats->rx_packets;
+ stats->tx_bytes = u64_stats_read(&mib->tx_good_bytes) -
+ ETH_FCS_LEN * stats->tx_packets;
+ stats->rx_dropped = u64_stats_read(&mib->rx_dropped);
+ /* stats->tx_dropped */
+ stats->multicast = u64_stats_read(&mib->rx_multicast);
+ stats->collisions = u64_stats_read(&mib->tx_collisions);
+ } while (u64_stats_fetch_retry(&pp->syncp, start));

- stats->rx_length_errors = mib->rx_undersize_errors +
- mib->rx_fragment_errors;
- stats->rx_over_errors = mib->rx_oversize_errors;
- stats->rx_crc_errors = mib->rx_crc_errors;
- stats->rx_frame_errors = mib->rx_alignment_errors;
- /* stats->rx_fifo_errors */
- /* stats->rx_missed_errors */
-
- stats->tx_aborted_errors = mib->tx_aborted_errors;
- /* stats->tx_carrier_errors */
- stats->tx_fifo_errors = mib->tx_undersize_errors;
- /* stats->tx_heartbeat_errors */
- stats->tx_window_errors = mib->tx_late_collisions;
-
- stats->rx_packets = pp->rx_frames;
- stats->tx_packets = pp->tx_frames;
- stats->rx_bytes = mib->rx_good_bytes - ETH_FCS_LEN * stats->rx_packets;
- stats->tx_bytes = mib->tx_good_bytes - ETH_FCS_LEN * stats->tx_packets;
stats->rx_errors = stats->rx_length_errors + stats->rx_over_errors +
stats->rx_crc_errors + stats->rx_frame_errors;
stats->tx_errors = stats->tx_aborted_errors + stats->tx_fifo_errors +
stats->tx_window_errors;
- stats->rx_dropped = mib->rx_dropped;
- /* stats->tx_dropped */
- stats->multicast = mib->rx_multicast;
- stats->collisions = mib->tx_collisions;
}

static void
@@ -941,13 +986,18 @@ yt921x_dsa_get_pause_stats(struct dsa_switch *ds, int port,
struct yt921x_priv *priv = to_yt921x_priv(ds);
struct yt921x_port *pp = &priv->ports[port];
struct yt921x_mib *mib = &pp->mib;
+ unsigned int start;

mutex_lock(&priv->reg_lock);
yt921x_read_mib(priv, port);
mutex_unlock(&priv->reg_lock);

- pause_stats->tx_pause_frames = mib->tx_pause;
- pause_stats->rx_pause_frames = mib->rx_pause;
+ do {
+ start = u64_stats_fetch_begin(&pp->syncp);
+
+ pause_stats->tx_pause_frames = u64_stats_read(&mib->tx_pause);
+ pause_stats->rx_pause_frames = u64_stats_read(&mib->rx_pause);
+ } while (u64_stats_fetch_retry(&pp->syncp, start));
}

static int
diff --git a/drivers/net/dsa/yt921x.h b/drivers/net/dsa/yt921x.h
index 61bb0ab3b09a..17fee83952c2 100644
--- a/drivers/net/dsa/yt921x.h
+++ b/drivers/net/dsa/yt921x.h
@@ -6,6 +6,8 @@
#ifndef __YT921X_H
#define __YT921X_H

+#include <linux/u64_stats_sync.h>
+
#include <net/dsa.h>

#define YT921X_SMI_SWITCHID_M GENMASK(3, 2)
@@ -475,55 +477,55 @@ enum yt921x_fdb_entry_status {
#define yt921x_port_is_external(port) (8 <= (port) && (port) < 9)

struct yt921x_mib {
- u64 rx_broadcast;
- u64 rx_pause;
- u64 rx_multicast;
- u64 rx_crc_errors;
-
- u64 rx_alignment_errors;
- u64 rx_undersize_errors;
- u64 rx_fragment_errors;
- u64 rx_64byte;
-
- u64 rx_65_127byte;
- u64 rx_128_255byte;
- u64 rx_256_511byte;
- u64 rx_512_1023byte;
-
- u64 rx_1024_1518byte;
- u64 rx_jumbo;
- u64 rx_good_bytes;
-
- u64 rx_bad_bytes;
- u64 rx_oversize_errors;
-
- u64 rx_dropped;
- u64 tx_broadcast;
- u64 tx_pause;
- u64 tx_multicast;
-
- u64 tx_undersize_errors;
- u64 tx_64byte;
- u64 tx_65_127byte;
- u64 tx_128_255byte;
-
- u64 tx_256_511byte;
- u64 tx_512_1023byte;
- u64 tx_1024_1518byte;
- u64 tx_jumbo;
-
- u64 tx_good_bytes;
- u64 tx_collisions;
-
- u64 tx_aborted_errors;
- u64 tx_multiple_collisions;
- u64 tx_single_collisions;
- u64 tx_good;
-
- u64 tx_deferred;
- u64 tx_late_collisions;
- u64 rx_oam;
- u64 tx_oam;
+ u64_stats_t rx_broadcast;
+ u64_stats_t rx_pause;
+ u64_stats_t rx_multicast;
+ u64_stats_t rx_crc_errors;
+
+ u64_stats_t rx_alignment_errors;
+ u64_stats_t rx_undersize_errors;
+ u64_stats_t rx_fragment_errors;
+ u64_stats_t rx_64byte;
+
+ u64_stats_t rx_65_127byte;
+ u64_stats_t rx_128_255byte;
+ u64_stats_t rx_256_511byte;
+ u64_stats_t rx_512_1023byte;
+
+ u64_stats_t rx_1024_1518byte;
+ u64_stats_t rx_jumbo;
+ u64_stats_t rx_good_bytes;
+
+ u64_stats_t rx_bad_bytes;
+ u64_stats_t rx_oversize_errors;
+
+ u64_stats_t rx_dropped;
+ u64_stats_t tx_broadcast;
+ u64_stats_t tx_pause;
+ u64_stats_t tx_multicast;
+
+ u64_stats_t tx_undersize_errors;
+ u64_stats_t tx_64byte;
+ u64_stats_t tx_65_127byte;
+ u64_stats_t tx_128_255byte;
+
+ u64_stats_t tx_256_511byte;
+ u64_stats_t tx_512_1023byte;
+ u64_stats_t tx_1024_1518byte;
+ u64_stats_t tx_jumbo;
+
+ u64_stats_t tx_good_bytes;
+ u64_stats_t tx_collisions;
+
+ u64_stats_t tx_aborted_errors;
+ u64_stats_t tx_multiple_collisions;
+ u64_stats_t tx_single_collisions;
+ u64_stats_t tx_good;
+
+ u64_stats_t tx_deferred;
+ u64_stats_t tx_late_collisions;
+ u64_stats_t rx_oam;
+ u64_stats_t tx_oam;
};

struct yt921x_port {
@@ -533,9 +535,13 @@ struct yt921x_port {
bool isolated;

struct delayed_work mib_read;
+ struct u64_stats_sync syncp;
struct yt921x_mib mib;
- u64 rx_frames;
- u64 tx_frames;
+ u64_stats_t rx_frames;
+ u64_stats_t tx_frames;
+
+ /* only used by read routine to avoid huge allocations on the stack */
+ struct yt921x_mib mib_new;
};

struct yt921x_reg_ops {
--
2.51.0