netdev - Re: [PATCH net-next v1 1/4] enetc: Clean up local mdio bus allocation

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Message-ID: <20190724163906.GT25635@lunn.ch>
Date:   Wed, 24 Jul 2019 18:39:06 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Claudiu Manoil <claudiu.manoil@....com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>, Leo Li <leoyang.li@....com>,
        Alexandru Marginean <alexandru.marginean@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v1 1/4] enetc: Clean up local mdio bus allocation

> >All the horrible casts go away, the driver is structured like every
> >other driver, sparse is probably happy, etc.
> >
> 
> This looks more like a matter cosmetic preferences.  I mean, I didn't
> notice anything "horrible" in the code so far.

#define bus_to_enetc_regs(bus)  (struct enetc_mdio_regs __iomem *)((bus)->priv)

You should not need a cast here, bus->priv is a void *. But bus->priv
is being abused to hold a __iomem pointer.

enetc_wr_reg(&regs->mdio_cfg, mdio_cfg);

This is also rather odd, passing the address of something to an IO
operator? I also don't know the C standard well enough to know if it
is guaranteed that:

struct enetc_mdio_regs {
        u32     mdio_cfg;       /* MDIO configuration and status */
        u32     mdio_ctl;       /* MDIO control */
        u32     mdio_data;      /* MDIO data */
        u32     mdio_addr;      /* MDIO address */
};

actually works. On a 64bit system is the compiler allowed to put in
padding to keep the u32 64 bit aligned?

> I actually find it more
> ugly to define a new structure with only one element inside, like:
> struct enetc_mdio_priv {
>        struct enetc_hw *hw;
> }

One advantage of this is that struct enetc_hw correctly has all the
__iomem attributes. All the casts to __iomem go away, and sparse is
happy.

> Anyway, if others already did this in the kernel, what can I do?

Clean it up. Make the code more readable and easy to maintain.

      Andrew