Merge branch 'net-ethernet-mtk-star-emac-fix-several-issues-on-rx-tx-poll'

Louis-Alexis Eyraud says:

====================
net: ethernet: mtk-star-emac: fix several issues on rx/tx poll

This patchset fixes two issues with the mtk-star-emac driver.

The first patch fixes spin lock recursion issues I've observed on the
Mediatek Genio 350-EVK board using this driver when the Ethernet
functionality is enabled on the board (requires a correct jumper and
DIP switch configuration, as well as enabling the device in the
devicetree).
The issues can be easily reproduced with apt install or ssh commands
especially and with the CONFIG_DEBUG_SPINLOCK parameter, when
one occurs, there is backtrace similar to this:
```
BUG: spinlock recursion on CPU#0, swapper/0/0
 lock: 0xffff00000db9cf20, .magic: dead4ead, .owner: swapper/0/0,
	.owner_cpu: 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted
	6.15.0-rc2-next-20250417-00001-gf6a27738686c-dirty #28 PREEMPT
Hardware name: MediaTek MT8365 Open Platform EVK (DT)
Call trace:
 show_stack+0x18/0x24 (C)
 dump_stack_lvl+0x60/0x80
 dump_stack+0x18/0x24
 spin_dump+0x78/0x88
 do_raw_spin_lock+0x11c/0x120
 _raw_spin_lock+0x20/0x2c
 mtk_star_handle_irq+0xc0/0x22c [mtk_star_emac]
 __handle_irq_event_percpu+0x48/0x140
 handle_irq_event+0x4c/0xb0
 handle_fasteoi_irq+0xa0/0x1bc
 handle_irq_desc+0x34/0x58
 generic_handle_domain_irq+0x1c/0x28
 gic_handle_irq+0x4c/0x120
 do_interrupt_handler+0x50/0x84
 el1_interrupt+0x34/0x68
 el1h_64_irq_handler+0x18/0x24
 el1h_64_irq+0x6c/0x70
 regmap_mmio_read32le+0xc/0x20 (P)
 _regmap_bus_reg_read+0x6c/0xac
 _regmap_read+0x60/0xdc
 regmap_read+0x4c/0x80
 mtk_star_rx_poll+0x2f4/0x39c [mtk_star_emac]
 __napi_poll+0x38/0x188
 net_rx_action+0x164/0x2c0
 handle_softirqs+0x100/0x244
 __do_softirq+0x14/0x20
 ____do_softirq+0x10/0x20
 call_on_irq_stack+0x24/0x64
 do_softirq_own_stack+0x1c/0x40
 __irq_exit_rcu+0xd4/0x10c
 irq_exit_rcu+0x10/0x1c
 el1_interrupt+0x38/0x68
 el1h_64_irq_handler+0x18/0x24
 el1h_64_irq+0x6c/0x70
 cpuidle_enter_state+0xac/0x320 (P)
 cpuidle_enter+0x38/0x50
 do_idle+0x1e4/0x260
 cpu_startup_entry+0x34/0x3c
 rest_init+0xdc/0xe0
 console_on_rootfs+0x0/0x6c
 __primary_switched+0x88/0x90
```

The second patch is a cleanup patch to fix a inconsistency in the
mtk_star_rx_poll function between the napi_complete_done api usage and
its description in documentation.

I've tested this patchset on Mediatek Genio 350-EVK board with a kernel
based on linux-next (tag: next-20250422).

v1: https://lore.kernel.org/20250422-mtk_star_emac-fix-spinlock-recursion-issue-v1-0-1e94ea430360@collabora.com
====================

Link: https://patch.msgid.link/20250424-mtk_star_emac-fix-spinlock-recursion-issue-v2-0-f3fde2e529d8@collabora.com
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

drivers/net/ethernet/mediatek/mtk_star_emac.c

@@ -1163,6 +1163,7 @@ static int mtk_star_tx_poll(struct napi_struct *napi, int budget)
 	struct net_device *ndev = priv->ndev;
 	unsigned int head = ring->head;
 	unsigned int entry = ring->tail;
+	unsigned long flags;
 
 	while (entry != head && count < (MTK_STAR_RING_NUM_DESCS - 1)) {
 		ret = mtk_star_tx_complete_one(priv);
@@ -1182,9 +1183,9 @@ static int mtk_star_tx_poll(struct napi_struct *napi, int budget)
 		netif_wake_queue(ndev);
 
 	if (napi_complete(napi)) {
-		spin_lock(&priv->lock);
+		spin_lock_irqsave(&priv->lock, flags);
 		mtk_star_enable_dma_irq(priv, false, true);
-		spin_unlock(&priv->lock);
+		spin_unlock_irqrestore(&priv->lock, flags);
 	}
 
 	return 0;
@@ -1341,16 +1342,16 @@ static int mtk_star_rx(struct mtk_star_priv *priv, int budget)
 static int mtk_star_rx_poll(struct napi_struct *napi, int budget)
 {
 	struct mtk_star_priv *priv;
+	unsigned long flags;
 	int work_done = 0;
 
 	priv = container_of(napi, struct mtk_star_priv, rx_napi);
 
 	work_done = mtk_star_rx(priv, budget);
-	if (work_done < budget) {
-		napi_complete_done(napi, work_done);
-		spin_lock(&priv->lock);
+	if (work_done < budget && napi_complete_done(napi, work_done)) {
+		spin_lock_irqsave(&priv->lock, flags);
 		mtk_star_enable_dma_irq(priv, true, false);
-		spin_unlock(&priv->lock);
+		spin_unlock_irqrestore(&priv->lock, flags);
 	}
 
 	return work_done;