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

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Message-ID: <CABb+yY2Ay+KqviJvOQC8X8kfzJN6-fQT04A+TCJAkLnWx+XwZg@mail.gmail.com>
Date: Sat, 20 Sep 2025 23:02:37 -0500
From: Jassi Brar <jassisinghbrar@...il.com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: Chen-Yu Tsai <wenst@...omium.org>, linux-mediatek@...ts.infradead.org, 
	Jjian Zhou <jjian.zhou@...iatek.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v5 2/2] mailbox: mediatek: Add mtk-vcp-mailbox driver

On Fri, Sep 19, 2025 at 2:02 PM Nicolas Frattaroli
<nicolas.frattaroli@...labora.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@...omium.org> wrote:
> > >
> > > On Fri, Sep 19, 2025 at 7:50 AM Jassi Brar <jassisinghbrar@...il.com> wrote:
> > > >
> > > > On Thu, Aug 21, 2025 at 9:12 PM Jjian Zhou <jjian.zhou@...iatek.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