Hi Sergei,
Thanks for your feedback.
On 2018-02-13 13:01:04 +0300, Sergei Shtylyov wrote:
> Hello!
>
> 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.
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 :-)
>
> [...]
> > @@ -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... And why add 16?
And +16 is added as the comment above states, to leave from the
descriptor status appended by the hardware. 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
agree? If in deed the FSC is not added I think we should fix this for
both drivers in a follow up commit.
>
> [...]
>
> MBR, Sergei
--
Regards,
Niklas Söderlund
