From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: 64-bit DMA
To: Vitaliy Makkoveev <mvs@openbsd.org>
Cc: tech@openbsd.org
Date: Wed, 25 Feb 2026 14:09:11 +0100

> Date: Wed, 25 Feb 2026 12:50:37 +0000
> From: Vitaliy Makkoveev <mvs@openbsd.org>
> 
> re(4) supports 64-bit DMA. Tested with
> 
> re0 at pci3 dev 0 function 0 "Realtek 8168" rev 0x11: RTL8168G/8111G
> (0x4c00), msi

Not quite as easy I fear.  Older PCI variants apparently may have
issues with dual address cycle (DAC) transactions.

> Index: sys/dev/ic/re.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/ic/re.c,v
> diff -u -p -r1.220 re.c
> --- sys/dev/ic/re.c	10 May 2025 11:08:26 -0000	1.220
> +++ sys/dev/ic/re.c	25 Feb 2026 12:44:27 -0000
> @@ -913,7 +913,7 @@ re_attach(struct rl_softc *sc, const cha
>  	if ((error = bus_dmamem_alloc(sc->sc_dmat, RL_TX_LIST_SZ(sc),
>  		    RL_RING_ALIGN, 0, &sc->rl_ldata.rl_tx_listseg, 1,
>  		    &sc->rl_ldata.rl_tx_listnseg, BUS_DMA_NOWAIT |
> -		    BUS_DMA_ZERO)) != 0) {
> +		    BUS_DMA_ZERO | BUS_DMA_64BIT)) != 0) {
>  		printf("%s: can't allocate tx listseg, error = %d\n",
>  		    sc->sc_dev.dv_xname, error);
>  		goto fail_0;
> @@ -930,7 +930,7 @@ re_attach(struct rl_softc *sc, const cha
>  	}
>  
>  	if ((error = bus_dmamap_create(sc->sc_dmat, RL_TX_LIST_SZ(sc), 1,
> -		    RL_TX_LIST_SZ(sc), 0, 0,
> +		    RL_TX_LIST_SZ(sc), 0, BUS_DMA_64BIT,
>  		    &sc->rl_ldata.rl_tx_list_map)) != 0) {
>  		printf("%s: can't create tx list map, error = %d\n",
>  		    sc->sc_dev.dv_xname, error);
> @@ -949,7 +949,7 @@ re_attach(struct rl_softc *sc, const cha
>  	for (i = 0; i < sc->rl_ldata.rl_tx_desc_cnt; i++) {
>  		error = bus_dmamap_create(sc->sc_dmat,
>  		    RL_JUMBO_FRAMELEN, sc->rl_ldata.rl_tx_ndescs,
> -		    RL_JUMBO_FRAMELEN, 0, 0,
> +		    RL_JUMBO_FRAMELEN, 0, BUS_DMA_64BIT,
>  		    &sc->rl_ldata.rl_txq[i].txq_dmamap);
>  		if (error) {
>  			printf("%s: can't create DMA map for TX\n",
> @@ -962,7 +962,7 @@ re_attach(struct rl_softc *sc, const cha
>  	if ((error = bus_dmamem_alloc(sc->sc_dmat, RL_RX_DMAMEM_SZ(sc),
>  		    RL_RING_ALIGN, 0, &sc->rl_ldata.rl_rx_listseg, 1,
>  		    &sc->rl_ldata.rl_rx_listnseg, BUS_DMA_NOWAIT |
> -		    BUS_DMA_ZERO)) != 0) {
> +		    BUS_DMA_ZERO | BUS_DMA_64BIT)) != 0) {
>  		printf("%s: can't allocate rx listnseg, error = %d\n",
>  		    sc->sc_dev.dv_xname, error);
>  		goto fail_4;
> @@ -980,7 +980,7 @@ re_attach(struct rl_softc *sc, const cha
>  	}
>  
>  	if ((error = bus_dmamap_create(sc->sc_dmat, RL_RX_DMAMEM_SZ(sc), 1,
> -		    RL_RX_DMAMEM_SZ(sc), 0, 0,
> +		    RL_RX_DMAMEM_SZ(sc), 0, BUS_DMA_64BIT,
>  		    &sc->rl_ldata.rl_rx_list_map)) != 0) {
>  		printf("%s: can't create rx list map, error = %d\n",
>  		    sc->sc_dev.dv_xname, error);
> @@ -999,7 +999,7 @@ re_attach(struct rl_softc *sc, const cha
>  	for (i = 0; i < sc->rl_ldata.rl_rx_desc_cnt; i++) {
>  		error = bus_dmamap_create(sc->sc_dmat,
>  		    RL_FRAMELEN(sc->rl_max_mtu), 1,
> -		    RL_FRAMELEN(sc->rl_max_mtu), 0, 0,
> +		    RL_FRAMELEN(sc->rl_max_mtu), 0, BUS_DMA_64BIT,
>  		    &sc->rl_ldata.rl_rxsoft[i].rxs_dmamap);
>  		if (error) {
>  			printf("%s: can't create DMA map for RX\n",
> 
>