Hi Sergey Shtylyov,
> Subject: Re: [PATCH 06/13] net: ravb: Let IP specific receive function to
> interrogate descriptors
>
> On 11/23/23 7:48 PM, Biju Das wrote:
> [...]
>
> >>> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >>>
> >>> ravb_poll() initial code used to interrogate the first descriptor of
> >>> the RX queue in case gptp is false to know if ravb_rx() should be
> >> called.
> >>> This is done for non GPTP IPs. For GPTP IPs the driver PTP specific
> >>
> >> It's called gPTP, AFAIK.
> >>
> >>> information was used to know if receive function should be called.
> >>> As every IP has it's own receive function that interrogates the RX
> >>> descriptor
> >>
> >> Its own.
> >>
> >>> list in the same way the ravb_poll() was doing there is no need to
> >>> double check this in ravb_poll(). Removing the code form ravb_poll()
> >>> and
> >>
> >> From ravb_poll().
> >>
> >>> adjusting ravb_rx_gbeth() leads to a cleaner code.
> >>>
> >>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >>> ---
> >>> drivers/net/ethernet/renesas/ravb_main.c | 18 ++++++------------
> >>> 1 file changed, 6 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c
> >>> b/drivers/net/ethernet/renesas/ravb_main.c
> >>> index 588e3be692d3..0fc9810c5e78 100644
> >>> --- a/drivers/net/ethernet/renesas/ravb_main.c
> >>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> >>> @@ -771,12 +771,15 @@ static bool ravb_rx_gbeth(struct net_device
> >>> *ndev,
> >> int *quota, int q)
> >>> int limit;
> >>>
> >>> entry = priv->cur_rx[q] % priv->num_rx_ring[q];
> >>> + desc = &priv->gbeth_rx_ring[entry];
> >>> + if (desc->die_dt == DT_FEMPTY)
> >>> + return false;
> >>> +
> >>
> >> I don't understand what this buys us, the following *while* loop
> >> will be skipped anyway, and the *for* loop as well, I think... And
> >> ravb_rx_rcar() doesn't have that anyway...
> >>
> >>> @@ -1279,25 +1282,16 @@ static int ravb_poll(struct napi_struct
> >>> *napi,
> >> int budget)
> >>> struct net_device *ndev = napi->dev;
> >>> struct ravb_private *priv = netdev_priv(ndev);
> >>> const struct ravb_hw_info *info = priv->info;
> >>> - bool gptp = info->gptp || info->ccc_gac;
> >>> - struct ravb_rx_desc *desc;
> >>> unsigned long flags;
> >>> int q = napi - priv->napi;
> >>> int mask = BIT(q);
> >>> int quota = budget;
> >>> - unsigned int entry;
> >>>
> >>> - if (!gptp) {
> >>> - entry = priv->cur_rx[q] % priv->num_rx_ring[q];
> >>> - desc = &priv->gbeth_rx_ring[entry];
> >>> - }
> >>> /* Processing RX Descriptor Ring */
> >>> /* Clear RX interrupt */
> >>> ravb_write(ndev, ~(mask | RIS0_RESERVED), RIS0);
> >>> - if (gptp || desc->die_dt != DT_FEMPTY) {
> >>> - if (ravb_rx(ndev, "a, q))
> >>> - goto out;
> >>> - }
> >>
> >> I don't really understand this code (despite I've AKCed it)...
> >> Biju, could you explain this (well, you tried already but I don't buy
> >> it anymore)?
> >
> > It was initial version of the driver. Now Claudiu optimized.
>
> I fail to understand why you had (GBEth-specific) pre-conditions here
> to call ravb_rx()... and involving gPTP only further confused things...
Initial driver is based on a reference code/bsp driver and that code has this preconditions.
Maybe they have faced some race condition in rx path involving ring buffer/descriptor.
But so far we are not able to reproduce any race condition here. So it is safe to remove now.
Cheers,
Biju
