On Mon, Sep 22, 2025 at 2:17 AM Jjian Zhou (周建) [off-list ref] wrote:

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+       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;