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

["Jjian Zhou (周建)" <Jjian.Zhou@mediatek.com>]

On Tue, 2025-09-23 at 08:16 -0500, Jassi Brar wrote:
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> 
> On Mon, Sep 22, 2025 at 2:17 AM Jjian Zhou (周建) <
> Jjian.Zhou@mediatek.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;

OK. This seems to convey the same meaning as what Nicolas said.
I modify it to this format.
Thank you.