[PATCH net-next v3 1/2] net: ethernet: mtk_eth_soc: skip page_pool

[Sandeep Haemoon <sandeeph@loljews.com>]

page_pool hands out order-0 pages and the pool is created with
MTK_PP_MAX_BUF_SIZE as the maximum DMA length, so it can only back a ring
whose descriptor length (ring->buf_size) fits in that.

Gate the pool on ring->buf_size instead of ring->frag_size: frag_size is
computed with the netdev_alloc_frag() layout, whose headroom and
skb_shared_info footprint differ from the pool's, so a ring can pass a
frag_size <= PAGE_SIZE test while its descriptor length is already larger
than the pool can map.

This is preparation for the 9K support in the next patch.  Today every
ring is smaller than the pool's limit and the new condition is always
true, so there is no functional change; once the normal ring follows a
jumbo MTU it grows past the limit and takes the netdev_alloc_frag()/
mtk_max_lro_buf_alloc() path that is already there.

Link: https://github.com/mediatek/mtk-openwrt-feeds
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Sandeep Haemoon <sandeeph@loljews.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index ad0fdc413..f2b2fb113 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -2819,7 +2819,15 @@ 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)) {
+	/* page_pool hands out order-0 pages and caps the DMA mapping at
+	 * MTK_PP_MAX_BUF_SIZE, so it can only back a ring whose descriptor
+	 * length fits that.  Today every ring does; this is the preparation
+	 * for the 9K support in the next patch, where the normal ring grows
+	 * past the pool's limit and takes the netdev_alloc_frag()/
+	 * mtk_max_lro_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