After commit 2af6106ae949 ("net: stmmac: Introducing support for Page
Pool"), the driver always copies frames to get a better performance,
zero-copy for RX frames is no more, then these code turned to be
useless and users of ethtool may get confused about the unhandled
rx-copybreak parameter.

This patch mostly reverts
commit 22ad38381547 ("stmmac: do not perform zero-copy for rx frames")

Signed-off-by: Furong Xu <0x1207@gmail.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac.h  |  2 -
 .../ethernet/stmicro/stmmac/stmmac_ethtool.c  | 39 -------------------
 .../net/ethernet/stmicro/stmmac/stmmac_main.c |  5 ---
 3 files changed, 46 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index 1d86439b8a14..b8d631e559c0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -126,7 +126,6 @@ struct stmmac_rx_queue {
 	unsigned int cur_rx;
 	unsigned int dirty_rx;
 	unsigned int buf_alloc_num;
-	u32 rx_zeroc_thresh;
 	dma_addr_t dma_rx_phy;
 	u32 rx_tail_addr;
 	unsigned int state_saved;
@@ -266,7 +265,6 @@ struct stmmac_priv {
 	int sph_cap;
 	u32 sarc_type;
 
-	unsigned int rx_copybreak;
 	u32 rx_riwt[MTL_MAX_TX_QUEUES];
 	int hwts_rx_en;
 
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
index 1d77389ce953..16b4d8c21c90 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
@@ -1227,43 +1227,6 @@ static int stmmac_get_ts_info(struct net_device *dev,
 		return ethtool_op_get_ts_info(dev, info);
 }
 
-static int stmmac_get_tunable(struct net_device *dev,
-			      const struct ethtool_tunable *tuna, void *data)
-{
-	struct stmmac_priv *priv = netdev_priv(dev);
-	int ret = 0;
-
-	switch (tuna->id) {
-	case ETHTOOL_RX_COPYBREAK:
-		*(u32 *)data = priv->rx_copybreak;
-		break;
-	default:
-		ret = -EINVAL;
-		break;
-	}
-
-	return ret;
-}
-
-static int stmmac_set_tunable(struct net_device *dev,
-			      const struct ethtool_tunable *tuna,
-			      const void *data)
-{
-	struct stmmac_priv *priv = netdev_priv(dev);
-	int ret = 0;
-
-	switch (tuna->id) {
-	case ETHTOOL_RX_COPYBREAK:
-		priv->rx_copybreak = *(u32 *)data;
-		break;
-	default:
-		ret = -EINVAL;
-		break;
-	}
-
-	return ret;
-}
-
 static int stmmac_get_mm(struct net_device *ndev,
 			 struct ethtool_mm_state *state)
 {
@@ -1390,8 +1353,6 @@ static const struct ethtool_ops stmmac_ethtool_ops = {
 	.set_per_queue_coalesce = stmmac_set_per_queue_coalesce,
 	.get_channels = stmmac_get_channels,
 	.set_channels = stmmac_set_channels,
-	.get_tunable = stmmac_get_tunable,
-	.set_tunable = stmmac_set_tunable,
 	.get_link_ksettings = stmmac_ethtool_get_link_ksettings,
 	.set_link_ksettings = stmmac_ethtool_set_link_ksettings,
 	.get_mm = stmmac_get_mm,
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 16b8bcfa8b11..6bc10ffe7a2b 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -77,7 +77,6 @@ module_param(phyaddr, int, 0444);
 MODULE_PARM_DESC(phyaddr, "Physical device address");
 
 #define STMMAC_TX_THRESH(x)	((x)->dma_conf.dma_tx_size / 4)
-#define STMMAC_RX_THRESH(x)	((x)->dma_conf.dma_rx_size / 4)
 
 /* Limit to make sure XDP TX and slow path can coexist */
 #define STMMAC_XSK_TX_BUDGET_MAX	256
@@ -107,8 +106,6 @@ static int buf_sz = DEFAULT_BUFSIZE;
 module_param(buf_sz, int, 0644);
 MODULE_PARM_DESC(buf_sz, "DMA buffer size");
 
-#define	STMMAC_RX_COPYBREAK	256
-
 static const u32 default_msg_level = (NETIF_MSG_DRV | NETIF_MSG_PROBE |
 				      NETIF_MSG_LINK | NETIF_MSG_IFUP |
 				      NETIF_MSG_IFDOWN | NETIF_MSG_TIMER);
@@ -3927,8 +3924,6 @@ static int __stmmac_open(struct net_device *dev,
 		}
 	}
 
-	priv->rx_copybreak = STMMAC_RX_COPYBREAK;
-
 	buf_sz = dma_conf->dma_buf_sz;
 	for (int i = 0; i < MTL_MAX_TX_QUEUES; i++)
 		if (priv->dma_conf.tx_queue[i].tbs & STMMAC_TBS_EN)
-- 
2.34.1

From: Furong Xu <0x1207@gmail.com>
Date: Wed, 18 Dec 2024 16:34:07 +0800

> After commit 2af6106ae949 ("net: stmmac: Introducing support for Page
> Pool"), the driver always copies frames to get a better performance,
> zero-copy for RX frames is no more, then these code turned to be
> useless and users of ethtool may get confused about the unhandled
> rx-copybreak parameter.
> 
> This patch mostly reverts
> commit 22ad38381547 ("stmmac: do not perform zero-copy for rx frames")
> 
> Signed-off-by: Furong Xu <0x1207@gmail.com>

The patch itself is fine, *but*

> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac.h  |  2 -
>  .../ethernet/stmicro/stmmac/stmmac_ethtool.c  | 39 -------------------
>  .../net/ethernet/stmicro/stmmac/stmmac_main.c |  5 ---
>  3 files changed, 46 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> index 1d86439b8a14..b8d631e559c0 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> @@ -126,7 +126,6 @@ struct stmmac_rx_queue {
>  	unsigned int cur_rx;
>  	unsigned int dirty_rx;
>  	unsigned int buf_alloc_num;
> -	u32 rx_zeroc_thresh;
>  	dma_addr_t dma_rx_phy;

If sizeof(dma_addr_t) == 8, you're clearly introducing a 4-byte hole
here. Perhaps you could reshuffle the struct a bit to avoid this.

It's always good to inspect the .kos with pahole after modifying
structures to make sure there are no regressions.

>  	u32 rx_tail_addr;
>  	unsigned int state_saved;

Thanks,
Olek

On Wed, 18 Dec 2024 16:48:38 +0100 Alexander Lobakin wrote:
> If sizeof(dma_addr_t) == 8, you're clearly introducing a 4-byte hole
> here. Perhaps you could reshuffle the struct a bit to avoid this.
> 
> It's always good to inspect the .kos with pahole after modifying
> structures to make sure there are no regressions.

Pretty off topic but I have a dumb question - how do you dump a struct
with pahole using debug info or BTF from a random .ko?
Ever since pahole got converted to BTF modules stopped working for me :S
I never cared enough to check as most interesting stuff is built-in
in Meta's kernels but it annoys me every now and then..

From: Jakub Kicinski <kuba@kernel.org>
Date: Wed, 18 Dec 2024 16:42:06 -0800

> On Wed, 18 Dec 2024 16:48:38 +0100 Alexander Lobakin wrote:
>> If sizeof(dma_addr_t) == 8, you're clearly introducing a 4-byte hole
>> here. Perhaps you could reshuffle the struct a bit to avoid this.
>>
>> It's always good to inspect the .kos with pahole after modifying
>> structures to make sure there are no regressions.
> 
> Pretty off topic but I have a dumb question - how do you dump a struct
> with pahole using debug info or BTF from a random .ko?
> Ever since pahole got converted to BTF modules stopped working for me :S

Hmm...

I have this

CONFIG_DEBUG_INFO=y
# CONFIG_DEBUG_INFO_NONE is not set
# CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is not set
# CONFIG_DEBUG_INFO_DWARF4 is not set
CONFIG_DEBUG_INFO_DWARF5=y
# CONFIG_DEBUG_INFO_REDUCED is not set
# CONFIG_DEBUG_INFO_COMPRESSED_NONE is not set
# CONFIG_DEBUG_INFO_COMPRESSED_ZLIB is not set
CONFIG_DEBUG_INFO_COMPRESSED_ZSTD=y
# CONFIG_DEBUG_INFO_SPLIT is not set
CONFIG_DEBUG_INFO_BTF=y
CONFIG_DEBUG_INFO_BTF_MODULES=y

CONFIG_PAHOLE_VERSION=127
CONFIG_PAHOLE_HAS_SPLIT_BTF=y
CONFIG_PAHOLE_HAS_BTF_TAG=y
CONFIG_PAHOLE_HAS_LANG_EXCLUDE=y

enabled in .config, then I just do

$ pahole path/to/module.ko | less

and search for the struct :D

My pahole is korg Git HEAD.

> I never cared enough to check as most interesting stuff is built-in
> in Meta's kernels but it annoys me every now and then..

Thanks,
Olek