Re: git: 38cbdae33b7c - main - dwc: Rewrite barrier part
Date: Tue, 10 Oct 2023 18:21:21 UTC
On 10/6/23 1:06 PM, Emmanuel Vadot wrote:
> The branch main has been updated by manu:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=38cbdae33b7c3f772845c06f52b86c0ddeab6a17
>
> commit 38cbdae33b7c3f772845c06f52b86c0ddeab6a17
> Author: Emmanuel Vadot <manu@FreeBSD.org>
> AuthorDate: 2023-10-06 16:04:49 +0000
> Commit: Emmanuel Vadot <manu@FreeBSD.org>
> CommitDate: 2023-10-06 17:05:45 +0000
>
> dwc: Rewrite barrier part
>
> We only need a barrier after writing the OWN bit so everything is
> coherent for the DMA engine.
> ---
> sys/dev/dwc/dwc1000_dma.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/sys/dev/dwc/dwc1000_dma.c b/sys/dev/dwc/dwc1000_dma.c
> index f6baa0bd3e45..4f8ae088305a 100644
> --- a/sys/dev/dwc/dwc1000_dma.c
> +++ b/sys/dev/dwc/dwc1000_dma.c
> @@ -216,7 +216,6 @@ txdesc_setup(struct dwc_softc *sc, int idx, bus_addr_t paddr,
> sc->txdesc_ring[idx].addr1 = (uint32_t)(paddr);
> sc->txdesc_ring[idx].desc0 = desc0;
> sc->txdesc_ring[idx].desc1 = desc1;
> - wmb();
> sc->txdesc_ring[idx].desc0 |= TDESC0_OWN;
> wmb();
> }
> @@ -237,7 +236,6 @@ rxdesc_setup(struct dwc_softc *sc, int idx, bus_addr_t paddr)
> sc->rxdesc_ring[idx].desc1 = ERDESC1_RCH |
> MIN(MCLBYTES, ERDESC1_RBS1_MASK);
>
> - wmb();
> sc->rxdesc_ring[idx].desc0 = RDESC0_OWN;
> wmb();
> return (nidx);
> @@ -524,7 +522,6 @@ dma1000_rxfinish_locked(struct dwc_softc *sc)
>
> m = dwc_rxfinish_one(sc, desc, sc->rxbuf_map + idx);
> if (m == NULL) {
> - wmb();
> desc->desc0 = RDESC0_OWN;
> wmb();
> } else {
Hmm, are you sure? I suspect you removed the wrong barrier here. You want the
other writes to update other fields in the desc to post before the write that
sets TDESC0_OWN. The barrier after TDESC0_OWN is useless, but the one you removed
is probably the one that matters. In particular you don't want TDESC0_OWN to be
set when other writes (e.g. setting desc1) are not yet visible.
--
John Baldwin