Re: [PATCH net-next v5 4/6] net: xilinx: axienet: Add 10G/25G (XXV) ethernet support

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] net: xilinx: axienet: XXV RX path reads length from unpopulated
  DMA metadata
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commit 24a43162ada4308aadc24cc61461a6b384478cc3
Author: Suraj Gupta <suraj.gupta2@amd.com>

net: xilinx: axienet: Add 10G/25G (XXV) ethernet support

This commit adds support for the Xilinx 10G/25G (XXV) Ethernet MAC and
PCS/PMA to the AXI Ethernet driver via a new axienet_10g25g_config.

> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_xxv.c b/drivers/net/ethernet/xilinx/xilinx_axienet_xxv.c
> new file mode 100644
> index 0000000000000..3c204dbbf6aec
> --- /dev/null
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_xxv.c

[ ... ]

> +const struct axienet_config axienet_10g25g_config = {
> +	.jumbo = true,
> +	.sw_padding = true,
> +	.internal_pcs = true,
> +	.regs_n = XXV_REGS_N,
> +	.options = xxvenet_options,
> +	.clk_init = axienet_10g25g_clk_init,
> +	.probe_init = axienet_xxv_probe_init,
> +	.gt_reset = axienet_xxv_gt_reset,
> +	.mac_init = axienet_xxv_mac_init,
> +	.get_regs = axienet_xxv_get_regs,
> +	.phylink_set_caps = axienet_xxv_phylink_set_capabilities,
> +	.pcs_ops = &axienet_xxv_pcs_ops,
> +};

[Severity: High]
How does the XXV RX path determine the received frame length on the
dmaengine path?

axienet_10g25g_config leaves .non_dmaengine false, so XXV always uses
axienet_dma_rx_cb(), which gets the frame length from DMA metadata word
LEN_APP (APP word 4):

drivers/net/ethernet/xilinx/xilinx_axienet_main.c:axienet_dma_rx_cb() {
	...
	app_metadata = dmaengine_desc_get_metadata_ptr(skbuf_dma->desc, &meta_len,
						       &meta_max_len);
	...
	if (IS_ERR(app_metadata)) {
		...
		dev_kfree_skb_any(skb);
		lp->ndev->stats.rx_dropped++;
		goto rx_submit;
	}

	/* TODO: Derive app word index programmatically */
	rx_len = (app_metadata[LEN_APP] & 0xFFFF);
	skb_put(skb, rx_len);
	...
}

Unlike the 1G AXI Ethernet IP, the XXV Ethernet IP has no AXI4-Stream
status/control stream to populate APP word 4.  Without
xlnx,axistream-connected on the DMA node,
dmaengine_desc_get_metadata_ptr() returns ERR_PTR(-ENOTSUPP) and every
received frame is dropped; even if that property is set, APP word 4 is
never written by the XXV MAC, so skb_put() uses 0 or stale descriptor data
instead of the actual transfer length (such as lp->max_frm_size -
result->residue from dmaengine_tx_status()).

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261114182947.2908628-1-suraj.gupta2@amd.com?part=4