On Mon, Mar 23, 2020 at 2:22 PM Marek Vasut <ma...@denx.de> wrote: > > On 3/23/20 1:19 PM, Ramon Fried wrote: > > On Mon, Mar 23, 2020 at 2:00 PM Marek Vasut <ma...@denx.de> wrote: > >> > >> On 3/23/20 8:09 AM, Ramon Fried wrote: > >>> On Mon, Mar 23, 2020 at 3:45 AM Marek Vasut <ma...@denx.de> wrote: > >>>> > >>>> The DMA may attempt to write a DMA descriptor in the ring while it is > >>>> being updated. By writing the DMA descriptor buffer address to 0, it > >>>> is assured the DMA will not use such a buffer and the buffer can be > >>>> updated without any interference. > >>>> > >>>> Signed-off-by: Marek Vasut <ma...@denx.de> > >>>> Cc: Joe Hershberger <joe.hershber...@ni.com> > >>>> Cc: Patrice Chotard <patrice.chot...@st.com> > >>>> Cc: Patrick Delaunay <patrick.delau...@st.com> > >>>> Cc: Ramon Fried <rfried....@gmail.com> > >>>> Cc: Stephen Warren <swar...@nvidia.com> > >>>> --- > >>>> drivers/net/dwc_eth_qos.c | 4 +++- > >>>> 1 file changed, 3 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/net/dwc_eth_qos.c b/drivers/net/dwc_eth_qos.c > >>>> index 7dadb10fe7..c86b9d59a5 100644 > >>>> --- a/drivers/net/dwc_eth_qos.c > >>>> +++ b/drivers/net/dwc_eth_qos.c > >>>> @@ -1431,8 +1431,10 @@ static int eqos_free_pkt(struct udevice *dev, > >>>> uchar *packet, int length) > >>>> > >>>> rx_desc = &(eqos->rx_descs[eqos->rx_desc_idx]); > >>>> > >>>> + rx_desc->des0 = 0; > >>>> + mb(); > >>> Better use wmb() for better understanding your goal here ? > >> > >> The driver uses mb() all over the place, so I'm just keeping it > >> consistent here. > >> > >> But I wonder whether we even need all those barriers in this driver at all. > > In that case that's fine :) > > I mean, I am asking about the need for those barriers here, that's my > question here. Better safe than sorry. unless you have the means to test it to see if it doesn't break.
Thanks, Ramon.
