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 15:21:04 +0100

> Date: Wed, 25 Feb 2026 13:34:13 +0000
> From: Vitaliy Makkoveev <mvs@openbsd.org>
> 
> On Wed, Feb 25, 2026 at 02:09:11PM +0100, Mark Kettenis wrote:
> > > 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.
> 
> I have and old Core2 motherboard, and if I'm not wrong it has re(4)
> related NIC. Is it old enough?

Probably not.

> However is easy to separate PCIe devices and enable 64-bit DMA only
> for them.

That was the heuristic I was leaning towards.  The PCIe variants
should all work fine with 64-bit addresses.  And most machines with
old PCI variants will heve less than 4GB of physical memory.

ok kettenis@

> 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 13:27:01 -0000
> @@ -667,6 +667,8 @@ re_attach(struct rl_softc *sc, const cha
>  	int		error = 0, i;
>  	const struct re_revision *rr;
>  	const char	*re_name = NULL;
> +	int		bus_dma64 = sc->rl_flags |= RL_FLAG_PCIE ?
> +			    BUS_DMA_64BIT : 0;
>  
>  	sc->sc_hwrev = CSR_READ_4(sc, RL_TXCFG) & RL_TXCFG_HWREV;
>  
> @@ -913,7 +915,7 @@ 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_dma64)) != 0) {
>  		printf("%s: can't allocate tx listseg, error = %d\n",
>  		    sc->sc_dev.dv_xname, error);
>  		goto fail_0;
> @@ -930,7 +932,7 @@ 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_dma64,
>  		    &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 +951,7 @@ 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_dma64,
>  		    &sc->rl_ldata.rl_txq[i].txq_dmamap);
>  		if (error) {
>  			printf("%s: can't create DMA map for TX\n",
> @@ -962,7 +964,7 @@ 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_dma64)) != 0) {
>  		printf("%s: can't allocate rx listnseg, error = %d\n",
>  		    sc->sc_dev.dv_xname, error);
>  		goto fail_4;
> @@ -980,7 +982,7 @@ 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_dma64,
>  		    &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 +1001,7 @@ 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_dma64,
>  		    &sc->rl_ldata.rl_rxsoft[i].rxs_dmamap);
>  		if (error) {
>  			printf("%s: can't create DMA map for RX\n",
>