linux-kernel - Re: [PATCH v5 2/2] mailbox: mediatek: Add mtk-vcp-mailbox driver

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Message-ID: <CABb+yY2bYh70A=n9+XBBqthjngZP2D8ebFje-F9TN7K0c+fmMA@mail.gmail.com>
Date: Tue, 23 Sep 2025 08:16:53 -0500
From: Jassi Brar <jassisinghbrar@...il.com>
To: Jjian Zhou (周建) <Jjian.Zhou@...iatek.com>
Cc: "nicolas.frattaroli@...labora.com" <nicolas.frattaroli@...labora.com>, 
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "wenst@...omium.org" <wenst@...omium.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>, 
	Project_Global_Chrome_Upstream_Group <Project_Global_Chrome_Upstream_Group@...iatek.com>, 
	"robh@...nel.org" <robh@...nel.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, 
	"matthias.bgg@...il.com" <matthias.bgg@...il.com>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v5 2/2] mailbox: mediatek: Add mtk-vcp-mailbox driver

On Mon, Sep 22, 2025 at 2:17 AM Jjian Zhou (周建) <Jjian.Zhou@...iatek.com> wrote:
>

> > > > > >
> > > > > > > +       void __iomem *base;
> > > > > > > +       struct device *dev;
> > > > > > > +       struct mbox_controller mbox;
> > > > > > > +       const struct mtk_vcp_mbox_cfg *cfg;
> > > > > > > +       struct mtk_ipi_info ipi_recv;
> > > > > >
> > > > > > Maybe also have "struct mbox_chan chan[1]; " so that you
> > > > > > don't have to
> > > > > > allocate one during the probe.
> > > > > > Also if you have  "struct mbox_controller mbox;" as the first
> > > > > > member,
> > > > > > you could simply typecast that to get this structure.
> > > > > > Something like "struct mpfs_mbox" in mailbox-mpfs.c
> > > > >
> > > > > I read somewhere that this way of subclassing is not
> > > > > recommended.
> > > > > Instead the base class should explicitly not be the first
> > > > > member.
> > > > > And then container_of() should be used.
> > > > >
> > > > > I don't remember where I read this though. But I think the
> > > > > explicit
> > > > > container_of() is easier for understanding the intent.
> > > > >
> > > >
> > > > And how does container_of() work ? :)
> > > > typcasting the first member to its parent is the simplest form of
> > > > container_of.
> > > >
> > > > -j
> > > >
> > > >
> > >
> > > Which is why it's completely equivalent and since code is supposed
> > > to communicate meaning to humans, container_of should be used.
> > >
> >
> > Nobody is suggesting typecasting cfg, dev or anything else.
> > Typecasting between mailbox controllers is fine and arguably easier
> > on
> > the eyes than using a container_of.
> >
> > -j
>
> OK. How about:
> struct mtk_vcp_mbox *priv = (struct mtk_vcp_mbox *)chan->con_priv;
>
You don't need to typecast a void *. So simply do
    struct mtk_vcp_mbox *priv = chan->con_priv;