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

[Nicolas Frattaroli <nicolas.frattaroli@collabora.com>]

On Monday, 22 September 2025 09:17:27 Central European Summer Time Jjian Zhou (周建) wrote:
> On Sat, 2025-09-20 at 23:02 -0500, Jassi Brar wrote:
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> > 
> > 
> > On Fri, Sep 19, 2025 at 2:02 PM Nicolas Frattaroli
> > <nicolas.frattaroli@collabora.com> wrote:
> > > 
> > > On Friday, 19 September 2025 18:32:12 Central European Summer Time
> > > Jassi Brar wrote:
> > > > On Fri, Sep 19, 2025 at 3:31 AM Chen-Yu Tsai <wenst@chromium.org>
> > > > wrote:
> > > > > 
> > > > > On Fri, Sep 19, 2025 at 7:50 AM Jassi Brar <
> > > > > jassisinghbrar@gmail.com> wrote:
> > > > > > 
> > > > > > On Thu, Aug 21, 2025 at 9:12 PM Jjian Zhou <
> > > > > > jjian.zhou@mediatek.com> wrote:
> > > > > > 
> > > > > > .....
> > > > > > 
> > > > > > > +#include <linux/module.h>
> > > > > > > +#include <linux/of.h>
> > > > > > > +#include <linux/platform_device.h>
> > > > > > > +#include <linux/slab.h>
> > > > > > > +
> > > > > > > +struct mtk_vcp_mbox_priv {
> > > > > > 
> > > > > > Maybe 'mtk_vcp_mbox' is a more appropriate name ?
> > > > > > 
> > > > > > > +       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;
> 
> Thanks.
> 

An explicit cast would be worse, as at that point you're telling
C to completely ignore any semblance of a type system it has.