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

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Message-ID: <CAMuHMdUEeZjfJgpXpO6qcAyuGp64wxyxiuLjUosVcRfG8=2s6w@mail.gmail.com>
Date:   Mon, 23 Aug 2021 11:14:19 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Biju Das <biju.das.jz@...renesas.com>
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 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.

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?

    /*
     * 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