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

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Date:   Thu, 12 Aug 2021 08:13:17 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sergey Shtylyov <s.shtylyov@...russia.ru>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        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 Geert,

Thanks for the feedback.

> 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.

Sergei, What is your thoughts here? Please let me know.

Cheers,
Biju