[PATCH net-next v4 2/3] net: ethernet: mtk_eth_soc: skip page_pool

[Sandeep Haemoon]

The page_pool is created with order-0 pages and MTK_PP_MAX_BUF_SIZE as
the maximum DMA length, so it can only back a ring whose descriptor
length fits in that.

Gate the pool on ring->buf_size <= MTK_PP_MAX_BUF_SIZE and let larger
rings use the netdev_alloc_frag()/mtk_max_buf_alloc() path that already
exists.  ring->frag_size cannot serve as the limit: it follows the
netdev_alloc_frag() layout, whose headroom and skb_shared_info footprint
differ from the pool's, so a ring can have frag_size <= PAGE_SIZE while
its descriptor length is already larger than the pool can map.

With the current MTU limits every ring fits and the gate always passes;
it becomes active with the 9K jumbo support that follows, when the
shared rings grow past the limit.

Link: https://github.com/mediatek/mtk-openwrt-feeds
Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
Signed-off-by: Sandeep Haemoon <sandeeph@xxxxxxxxxxx>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index a46cf5441..6768ab8eb 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -2825,7 +2825,13 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
 	if (!ring->data)
 		return -ENOMEM;
 
-	if (mtk_page_pool_enabled(eth)) {
+	/* A page_pool hands out order-0 pages and is created with
+	 * MTK_PP_MAX_BUF_SIZE, so it can only back a ring whose descriptor
+	 * length fits.  Larger rings use the netdev_alloc_frag()/
+	 * mtk_max_buf_alloc() path below instead.
+	 */
+	if (mtk_page_pool_enabled(eth) &&
+	    ring->buf_size <= MTK_PP_MAX_BUF_SIZE) {
 		struct page_pool *pp;
 
 		pp = mtk_create_page_pool(eth, &ring->xdp_q, ring_no,
-- 
2.53.0