linux-kernel - Re: [PATCH net-next v3 3/7] net: lan966x: Add len field to lan966x_tx_dcb

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Date:   Tue, 22 Nov 2022 22:21:24 +0100
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <bpf@...r.kernel.org>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <ast@...nel.org>, <daniel@...earbox.net>, <hawk@...nel.org>,
        <john.fastabend@...il.com>, <UNGLinuxDriver@...rochip.com>
Subject: Re: [PATCH net-next v3 3/7] net: lan966x: Add len field to
 lan966x_tx_dcb_buf

The 11/22/2022 12:30, Alexander Lobakin wrote:
> 
> From: Horatiu Vultur <horatiu.vultur@...rochip.com>
> Date: Mon, 21 Nov 2022 22:28:46 +0100
> 
> > Currently when a frame was transmitted, it is required to unamp the
> > frame that was transmitted. The length of the frame was taken from the
> > transmitted skb. In the future we might not have an skb, therefore store
> > the length skb directly in the lan966x_tx_dcb_buf and use this one to
> > unamp the frame.
> >
> > Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> > ---
> >  drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 5 +++--
> >  drivers/net/ethernet/microchip/lan966x/lan966x_main.h | 1 +
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> > index 94c720e59caee..384ed34197d58 100644
> > --- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> > +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> > @@ -391,12 +391,12 @@ static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
> >                       continue;
> >
> >               dcb_buf->dev->stats.tx_packets++;
> > -             dcb_buf->dev->stats.tx_bytes += dcb_buf->skb->len;
> > +             dcb_buf->dev->stats.tx_bytes += dcb_buf->len;
> >
> >               dcb_buf->used = false;
> >               dma_unmap_single(lan966x->dev,
> >                                dcb_buf->dma_addr,
> > -                              dcb_buf->skb->len,
> > +                              dcb_buf->len,
> >                                DMA_TO_DEVICE);
> >               if (!dcb_buf->ptp)
> >                       dev_kfree_skb_any(dcb_buf->skb);
> > @@ -709,6 +709,7 @@ int lan966x_fdma_xmit(struct sk_buff *skb, __be32 *ifh, struct net_device *dev)
> >       /* Fill up the buffer */
> >       next_dcb_buf = &tx->dcbs_buf[next_to_use];
> >       next_dcb_buf->skb = skb;
> > +     next_dcb_buf->len = skb->len;
> >       next_dcb_buf->dma_addr = dma_addr;
> >       next_dcb_buf->used = true;
> >       next_dcb_buf->ptp = false;
> > diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> > index bc93051aa0798..7bb9098496f60 100644
> > --- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> > +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> > @@ -175,6 +175,7 @@ struct lan966x_rx {
> >  struct lan966x_tx_dcb_buf {
> >       struct net_device *dev;
> >       struct sk_buff *skb;
> > +     int len;
> 
> Nit: perhaps you can define it as `u32` since fram length can't be
> negative?

The length is always positive. I will update this in the next version.

> 
> >       dma_addr_t dma_addr;
> 
> Oh, also, on platforms with 64-bit addressing, `int len` placed in
> between ::skb and ::dma_addr would create a 4-byte hole in the
> structure. Placing `len` after ::dma_addr would make it holeless on
> any architercture.

Thanks for the suggestion.
I will make sure that lan966x_tx_dcb_buf will not have any holes. In
this patch I will arrange the members and in the next patches where
I will modify the struct, I will add them at the right place.

> 
> >       bool used;
> >       bool ptp;
> > --
> > 2.38.0
> 
> Thanks,
> Olek

-- 
/Horatiu