Re: [PATCH v3 net-next 5/5] net: fec: enable the Jumbo frame support for i.MX8QM

[Andrew Lunn]

> @@ -1278,8 +1280,16 @@ fec_restart(struct net_device *ndev)
>  	if (fep->quirks & FEC_QUIRK_ENET_MAC) {
>  		/* enable ENET endian swap */
>  		ecntl |= FEC_ECR_BYTESWP;
> -		/* enable ENET store and forward mode */
> -		writel(FEC_TXWMRK_STRFWD, fep->hwp + FEC_X_WMRK);
> +
> +		/* When Jumbo Frame is enabled, the FIFO may not be large enough
> +		 * to hold an entire frame. In this case, configure the interface
> +		 * to operate in cut-through mode, triggered by the FIFO threshold.
> +		 * Otherwise, enable the ENET store-and-forward mode.
> +		 */
> +		if (fep->quirks & FEC_QUIRK_JUMBO_FRAME)
> +			writel(0xF, fep->hwp + FEC_X_WMRK);

The quirk indicates the hardware is capable of jumbo frames, not that
jumbo frames are enabled. Don't you need to compare the mtu with
ETH_FRAME_LEN + ETH_FCS_LEN to say jumbo is enabled?

Is there a counter or other indication that the FIFO experienced an
underflow?

	Andrew