netdev - Re: [PATCH net-next v2 1/8] ravb: Add struct ravb_hw

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Date:   Thu, 12 Aug 2021 09:58:43 +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 v2 1/8] ravb: Add struct ravb_hw_info to driver data

Hi Biju,

On Thu, Aug 12, 2021 at 9:26 AM Biju Das <biju.das.jz@...renesas.com> wrote:
> > -----Original Message-----
> > On Mon, Aug 2, 2021 at 12:27 PM Biju Das <biju.das.jz@...renesas.com>
> > wrote:
> > > The DMAC and EMAC blocks of Gigabit Ethernet IP found on RZ/G2L SoC
> > > are similar to the R-Car Ethernet AVB IP. With a few changes in the
> > > driver we can support both IPs.
> > >
> > > Currently a runtime decision based on the chip type is used to
> > > distinguish the HW differences between the SoC families.
> > >
> > > The number of TX descriptors for R-Car Gen3 is 1 whereas on R-Car Gen2
> > > and RZ/G2L it is 2. For cases like this it is better to select the
> > > number of TX descriptors by using a structure with a value, rather
> > > than a runtime decision based on the chip type.
> > >
> > > This patch adds the num_tx_desc variable to struct ravb_hw_info and
> > > also replaces the driver data chip type with struct ravb_hw_info by
> > > moving chip type to it.
> > >
> > > Signed-off-by: Biju Das <biju.das.jz@...renesas.com>
> > > Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Thanks for your patch!
> >
> > > --- a/drivers/net/ethernet/renesas/ravb.h
> > > +++ b/drivers/net/ethernet/renesas/ravb.h
> > > @@ -988,6 +988,11 @@ enum ravb_chip_id {
> > >         RCAR_GEN3,
> > >  };
> > >
> > > +struct ravb_hw_info {
> > > +       enum ravb_chip_id chip_id;
> > > +       int num_tx_desc;
> >
> > Why not "unsigned int"? ...
> > This comment applies to a few more subsequent patches.
>
> To avoid signed and unsigned comparison warnings.
>
> >
> > > +};
> > > +
> > >  struct ravb_private {
> > >         struct net_device *ndev;
> > >         struct platform_device *pdev;
> > > @@ -1040,6 +1045,8 @@ struct ravb_private {
> > >         unsigned txcidm:1;              /* TX Clock Internal Delay Mode
> > */
> > >         unsigned rgmii_override:1;      /* Deprecated rgmii-*id behavior
> > */
> > >         int num_tx_desc;                /* TX descriptors per packet */
> >
> > ... oh, here's the original culprit.
>
> Exactly, this the reason.
>
> Do you want me to change this into unsigned int? Please let me know.

Up to you (or the maintainer? ;-)

For new fields (in the other patches), I would use unsigned for all
unsigned values.  Signed values have more pitfalls related to
undefined behavior.

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