netdev - RE: [PATCH net-next v3 3/9] ravb: Add aligned_tx to struct ravb_hw

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Date:   Mon, 23 Aug 2021 09:26:56 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Sergey Shtylyov <s.shtylyov@...russia.ru>,
        Adam Ford <aford173@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Yuusuke Ashizuka <ashiduka@...itsu.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: RE: [PATCH net-next v3 3/9] ravb: Add aligned_tx to struct
 ravb_hw_info

Hi Geert,

Thanks for the feedback

> Subject: Re: [PATCH net-next v3 3/9] ravb: Add aligned_tx to struct
> ravb_hw_info
> 
> Hi Biju,
> 
> On Wed, Aug 18, 2021 at 9:08 PM Biju Das <biju.das.jz@...renesas.com>
> wrote:
> > R-Car Gen2 needs a 4byte aligned address for the transmission buffer,
> > whereas R-Car Gen3 doesn't have any such restriction.
> >
> > Add aligned_tx to struct ravb_hw_info to select the driver to choose
> > between aligned and unaligned tx buffers.
> >
> > Signed-off-by: Biju Das <biju.das.jz@...renesas.com>
> > Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> 
> Thanks for your patch, which is now commit 68ca3c923213b908 ("ravb:
> Add aligned_tx to struct ravb_hw_info") in net-next.
> 
> > --- a/drivers/net/ethernet/renesas/ravb.h
> > +++ b/drivers/net/ethernet/renesas/ravb.h
> > @@ -990,6 +990,7 @@ enum ravb_chip_id {
> >
> >  struct ravb_hw_info {
> >         enum ravb_chip_id chip_id;
> > +       unsigned aligned_tx: 1;
> >  };
> >
> >  struct ravb_private {
> > diff --git a/drivers/net/ethernet/renesas/ravb_main.c
> > b/drivers/net/ethernet/renesas/ravb_main.c
> > index b6554e5e13af..dbccf2cd89b2 100644
> > --- a/drivers/net/ethernet/renesas/ravb_main.c
> > +++ b/drivers/net/ethernet/renesas/ravb_main.c
> > @@ -1930,6 +1930,7 @@ static const struct ravb_hw_info
> > ravb_gen3_hw_info = {
> >
> >  static const struct ravb_hw_info ravb_gen2_hw_info = {
> >         .chip_id = RCAR_GEN2,
> > +       .aligned_tx = 1,
> >  };
> >
> >  static const struct of_device_id ravb_match_table[] = { @@ -2140,7
> > +2141,7 @@ static int ravb_probe(struct platform_device *pdev)
> >         ndev->max_mtu = 2048 - (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
> >         ndev->min_mtu = ETH_MIN_MTU;
> >
> > -       priv->num_tx_desc = info->chip_id == RCAR_GEN2 ?
> > +       priv->num_tx_desc = info->aligned_tx ?
> >                 NUM_TX_DESC_GEN2 : NUM_TX_DESC_GEN3;
> 
> At first look, this change does not seem to match the patch description.
> Upon a deeper look, it is correct, as num_tx_desc is also used to control
> alignment.

This changes introduced by the commit [1], where it used num_tx_desc related to 4byte alignment restriction.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/net/ethernet/renesas/ravb_main.c?h=v5.14-rc7&id=f543305da9b5a5efaf6fa61606e8bbc8977f406d


> 
> But now NUM_TX_DESC_GEN[23] no longer match their use.
> Perhaps they should be renamed, or replaced by hardcoded values, with a
> comment?

OK, will replace this macros with hardcoded values with a comment.

Regards,
Biju


> 
>     /*
>      * FIXME: Explain the relationship between alignment and number of
> buffers
>      */
>     priv->num_tx_desc = info->aligned_tx ? 2 : 1;
> 
> >
> >         /* Set function */
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a hacker.
> But when I'm talking to journalists I just say "programmer" or something
> like that.
>                                 -- Linus Torvalds