[openwrt/openwrt] bcm53xx: copy bgmac revert (performance fix) to 5.15

[LEDE Commits]

rmilecki pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/d19c37486b1ce25f4215e1282a4025672b108201

commit d19c37486b1ce25f4215e1282a4025672b108201
Author: Rafał Miłecki <rafal at milecki.pl>
AuthorDate: Fri Jun 17 07:58:00 2022 +0200

    bcm53xx: copy bgmac revert (performance fix) to 5.15
    
    Ref: 230c9da963aa ("bcm53xx: revert bgmac back to the old limited max frame size")
    Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
 ...e-max-frame-size-to-support-just-MTU-1500.patch | 33 ++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/target/linux/bcm53xx/patches-5.15/700-bgmac-reduce-max-frame-size-to-support-just-MTU-1500.patch b/target/linux/bcm53xx/patches-5.15/700-bgmac-reduce-max-frame-size-to-support-just-MTU-1500.patch
new file mode 100644
index 0000000000..3a2f4b06ed
--- /dev/null
+++ b/target/linux/bcm53xx/patches-5.15/700-bgmac-reduce-max-frame-size-to-support-just-MTU-1500.patch
@@ -0,0 +1,33 @@
+From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal at milecki.pl>
+Date: Fri, 10 Jun 2022 13:10:47 +0200
+Subject: [PATCH] bgmac: reduce max frame size to support just MTU 1500
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+bgmac allocates new replacement buffer before handling each received
+frame. Allocating & DMA-preparing 9724 B each time consumes a lot of CPU
+time. Ideally bgmac should just respect currently set MTU but it isn't
+the case right now. For now just revert back to the old limited frame
+size.
+
+This change bumps NAT masquarade speed by ~95%.
+
+Ref: 8c7da63978f1 ("bgmac: configure MTU and add support for frames beyond 8192 byte size")
+Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
+---
+ drivers/net/ethernet/broadcom/bgmac.h | 3 +--
+ 1 file changed, 1 insertion(+), 2 deletions(-)
+
+--- a/drivers/net/ethernet/broadcom/bgmac.h
++++ b/drivers/net/ethernet/broadcom/bgmac.h
+@@ -328,8 +328,7 @@
+ #define BGMAC_RX_FRAME_OFFSET			30		/* There are 2 unused bytes between header and real data */
+ #define BGMAC_RX_BUF_OFFSET			(NET_SKB_PAD + NET_IP_ALIGN - \
+ 						 BGMAC_RX_FRAME_OFFSET)
+-/* Jumbo frame size with FCS */
+-#define BGMAC_RX_MAX_FRAME_SIZE			9724
++#define BGMAC_RX_MAX_FRAME_SIZE			1536
+ #define BGMAC_RX_BUF_SIZE			(BGMAC_RX_FRAME_OFFSET + BGMAC_RX_MAX_FRAME_SIZE)
+ #define BGMAC_RX_ALLOC_SIZE			(SKB_DATA_ALIGN(BGMAC_RX_BUF_SIZE + BGMAC_RX_BUF_OFFSET) + \
+ 						 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))