Re: [PATCH net-next v2 2/2] net: stmmac: dwmac-sun8i: Enable jumbo frames up to MTU 2018

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] net: stmmac: dwmac-sun8i: DT max-frame-size ignored in
  sun8i_dwmac_probe()
--

commit 51742ecb57f35bd210c0c45ef051593dd802ce68
Author: Arun Iyengar <aiyengar1990@gmail.com>

net: stmmac: dwmac-sun8i: Enable jumbo frames up to MTU 2018

This commit sets EMAC_RX_JUMBO_FRM_EN in sun8i_dwmac_core_init() and bounds
plat_dat->maxmtu to 2018 bytes so frames fit within a single 2044-byte DMA
descriptor buffer.

> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
> index 0c82662fbe6ea..a18d3daf6a3ff 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c

[ ... ]

> @@ -1209,6 +1232,7 @@ static int sun8i_dwmac_probe(struct platform_device *pdev)
>  	plat_dat->mac_setup = sun8i_dwmac_setup;
>  	plat_dat->tx_fifo_size = 4096;
>  	plat_dat->rx_fifo_size = 16384;
> +	plat_dat->maxmtu = min(plat_dat->maxmtu, EMAC_MAX_MTU);

[Severity: Medium]
Does min(plat_dat->maxmtu, EMAC_MAX_MTU) honor a device tree max-frame-size
property as intended?

devm_stmmac_probe_config_dt() initializes plat_dat->maxmtu to JUMBO_LEN
(9000), and stmmac_probe_config_dt() only reads max-frame-size for specific
compatibles:

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:stmmac_probe_config_dt() {
	...
	if (of_device_is_compatible(np, "st,spear600-gmac") ||
		of_device_is_compatible(np, "snps,dwmac-3.50a") ||
		of_device_is_compatible(np, "snps,dwmac-3.70a") ||
		of_device_is_compatible(np, "snps,dwmac-3.72a") ||
		of_device_is_compatible(np, "snps,dwmac")) {
		...
		of_property_read_u32(np, "max-frame-size", &plat->maxmtu);
	...
}

Because dwmac-sun8i device tree nodes only use allwinner,sun8i-* and
allwinner,sun50i-* compatibles, plat_dat->maxmtu is always JUMBO_LEN here and
a max-frame-size property in the device tree will never lower it below
EMAC_MAX_MTU.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261112-sun8i-emac-jumbo-v2-0-aca0cf23cf17@gmail.com?part=2