On 8/11/21 4:16 PM, Marc Zyngier wrote:

On Wed, 11 Aug 2021 13:53:59 +0100,
Eric Dumazet [off-list ref] wrote:

quoted

Are you sure you do not need to adjust stmmac_set_bfsize(), 
stmmac_rx_buf1_len() and stmmac_rx_buf2_len() ?

Presumably DEFAULT_BUFSIZE also want to be increased by NET_SKB_PAD

Patch for stmmac_rx_buf1_len() :

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 7b8404a21544cf29668e8a14240c3971e6bce0c3..041a74e7efca3436bfe3e17f972dd156173957a9 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -4508,12 +4508,12 @@ static unsigned int stmmac_rx_buf1_len(struct stmmac_priv *priv,
 
        /* First descriptor, not last descriptor and not split header */
        if (status & rx_not_ls)
-               return priv->dma_buf_sz;
+               return priv->dma_buf_sz - NET_SKB_PAD - NET_IP_ALIGN;
 
        plen = stmmac_get_rx_frame_len(priv, p, coe);
 
        /* First descriptor and last descriptor and not split header */
-       return min_t(unsigned int, priv->dma_buf_sz, plen);
+       return min_t(unsigned int, priv->dma_buf_sz - NET_SKB_PAD - NET_IP_ALIGN, plen);
 }
 
 static unsigned int stmmac_rx_buf2_len(struct stmmac_priv *priv,

Feels like a major deficiency of the original patch. Happy to test a
more complete patch if/when you have one.

I wont have time in the immediate future.

Matteo, if you do not work on a fix, I suggest we revert
 a955318fe67ec0d962760b5ee58e74bffaf649b8 stmmac: align RX buffers

before a more polished version can be submitted.