Hi Sergei,
Thanks for your feedback.
On 2018-02-14 14:34:09 +0300, Sergei Shtylyov wrote:
> Hello!
>
> On 02/13/2018 04:12 PM, Niklas Söderlund wrote:
>
> >> On 02/12/2018 11:00 PM, Niklas Söderlund wrote:
> >>
> >>> Allow for chancing the MTU within the limit of the maximum size of a
> >>
> >> Changing. :-)
> >
> > Yes :-)
> >
> >>> descriptor (2048 bytes). Add the callback to change MTU from user-space
> >>> and take the configurable MTU into account when configuring the
> >>> hardware.
> >>>
> >>> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> >> [...]
> >>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> >>> index c87f57ca44371586..a4870c9e42195802 100644
> >>> --- a/drivers/net/ethernet/renesas/ravb_main.c
> >>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> >>> @@ -300,9 +300,9 @@ static void ravb_ring_format(struct net_device *ndev, int q)
> >>> for (i = 0; i < priv->num_rx_ring[q]; i++) {
> >>> /* RX descriptor */
> >>> rx_desc = &priv->rx_ring[q][i];
> >>> - rx_desc->ds_cc = cpu_to_le16(PKT_BUF_SZ);
> >>> + rx_desc->ds_cc = cpu_to_le16(priv->rx_buf_sz);
> >>> dma_addr = dma_map_single(ndev->dev.parent, priv->rx_skb[q][i]->data,
> >>> - PKT_BUF_SZ,
> >>> + le16_to_cpu(rx_desc->ds_cc),
> >>
> >> Why not 'priv->rx_buf_sz'?
> >
> > To align the arguments used with the one in ravb_rx() which uses
> > le16_to_cpu(rx_desc->ds_cc) already before this patch.
>
> Why?
>
> > static bool ravb_rx(struct net_device *ndev, int *quota, int q)
> > {
> > ...
> > /* Refill the RX ring buffers. */
> > for (; priv->cur_rx[q] - priv->dirty_rx[q] > 0; priv->dirty_rx[q]++) {
> > ...
> > desc->ds_cc = cpu_to_le16(priv->rx_buf_sz);
> >
> > if (!priv->rx_skb[q][entry]) {
> > ...
> > dma_addr = dma_map_single(ndev->dev.parent, skb->data,
> > le16_to_cpu(desc->ds_cc),
> > DMA_FROM_DEVICE);
> > ...
> > }
> > ...
> > }
> > ...
> > }
> >
> > I have no preference one way or the other but I think both call sites
> > should look the same :-)
>
> Why? I don't like this idea at all...
OK, I will use 'priv->rx_buf_sz' in next version. But I still think it's
confusing to not align the call sites :-)
>
> >> [...]
> >>> @@ -346,6 +346,10 @@ static int ravb_ring_init(struct net_device *ndev, int q)
> >>> int ring_size;
> >>> int i;
> >>>
> >>> + /* +16 gets room from the status from the card. */
> >>> + priv->rx_buf_sz = (ndev->mtu <= 1492 ? PKT_BUF_SZ : ndev->mtu) +
> >>> + ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN + 16;
> >>
> >> Mhm, I don't think FCS gets added to the frame buffer...
>
> It certainly isn't included, judging by the manuals... Instead 2-byte checksum is
> included after the frame data (if checksumming is enabled).
OK, I will drop ETH_FCS_LEN from v2. Would you like a similar patch for
sh_eth ?
>
> > And why add 16?
> >
> > And +16 is added as the comment above states, to leave from the
> > descriptor status appended by the hardware.
>
> I don't see any appended status in the manuals, do you?
You are correct, looks like I misunderstood the docs, I was thinking of
the descriptor described in 50.4.4 (7) but I now see that is handled
differently, will drop the +16 for v2. Thanks for spotting this!
>
> > This is already the case
> > with PKT_BUF_SZ which for ravb is is set to 1538. MTU (1500) + ETH_HLEN
> > (14) + VLAN_HLEN(4) + ETH_FCS_LEN(4) + ravb status (16) == 1538.
>
> > This is also what the sh_eth driver do and I think it's value to keep
> > these to driver as similar as possible in this regard, would you not
>
> The DMA hardware is totally different, so I don't see any value in mirroring what sh_eth does...
>
> > agree? If in deed the FSC is not added I think we should fix this for
> > both drivers in a follow up commit.
>
> Probably a good idea... :-)
>
> [...]
>
> MBR, Sergei
--
Regards,
Niklas Söderlund
