linux-kernel - RE: [PATCH net-next 1/3] enetc: Add mdio bus driver for the PCIe MDIO endpoint

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Date:   Wed, 24 Jul 2019 12:57:34 +0000
From:   Claudiu Manoil <claudiu.manoil@....com>
To:     Claudiu Manoil <claudiu.manoil@....com>,
        Andrew Lunn <andrew@...n.ch>
CC:     "David S . Miller" <davem@...emloft.net>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexandru Marginean <alexandru.marginean@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Leo Li <leoyang.li@....com>, Rob Herring <robh+dt@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH net-next 1/3] enetc: Add mdio bus driver for the PCIe MDIO
 endpoint



>-----Original Message-----
>From: netdev-owner@...r.kernel.org <netdev-owner@...r.kernel.org> On
>Behalf Of Claudiu Manoil
>Sent: Wednesday, July 24, 2019 12:53 PM
>To: Andrew Lunn <andrew@...n.ch>
>Cc: David S . Miller <davem@...emloft.net>; devicetree@...r.kernel.org;
>netdev@...r.kernel.org; Alexandru Marginean
><alexandru.marginean@....com>; linux-kernel@...r.kernel.org; Leo Li
><leoyang.li@....com>; Rob Herring <robh+dt@...nel.org>; linux-arm-
>kernel@...ts.infradead.org
>Subject: RE: [PATCH net-next 1/3] enetc: Add mdio bus driver for the PCIe MDIO
>endpoint
>
>>-----Original Message-----
>>From: Andrew Lunn <andrew@...n.ch>
>>Sent: Wednesday, July 24, 2019 1:25 AM
>>To: Claudiu Manoil <claudiu.manoil@....com>
>>Cc: David S . Miller <davem@...emloft.net>; devicetree@...r.kernel.org;
>>netdev@...r.kernel.org; Alexandru Marginean
>><alexandru.marginean@....com>; linux-kernel@...r.kernel.org; Leo Li
>><leoyang.li@....com>; Rob Herring <robh+dt@...nel.org>; linux-arm-
>>kernel@...ts.infradead.org
>>Subject: Re: [PATCH net-next 1/3] enetc: Add mdio bus driver for the
>>PCIe MDIO endpoint
>>
>>> +	bus = mdiobus_alloc_size(sizeof(u32 *));
>>> +	if (!bus)
>>> +		return -ENOMEM;
>>> +
>>
>>> +	bus->priv = pci_iomap_range(pdev, 0, ENETC_MDIO_REG_OFFSET, 0);
>>
>>This got me confused for a while. You allocate space for a u32 pointer.
>>bus->priv will point to this space. However, you are not using this
>>space, you {ab}use the pointer to directly hold the return from
>>pci_iomap_range(). This works, but sparse is probably unhappy, and you
>>are wasting the space the u32 pointer takes.
>>
>
>Thanks Andrew,
>This is not what I wanted to do, don't ask me how I got to this, it's confusing
>indeed.
>What's needed here is mdiobus_alloc() or better, devm_mdiobus_alloc().
>I've got to do some cleanup in the local mdio bus probing too.
>Will send v2.
>

This is tricky actually, mdiobus_alloc won't do it, I still need to allocate space
for the pointer.
So it's not ok to store the register space pointer directly into priv
(even if iomap returns void *), it's unusual.
Looks like I will have to use double pointers!