linux-kernel - Re: [PATCH v12 1/7] mfd: Add core driver for Nuvoton NCT6694

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Message-ID: <20250613131133.GR381401@google.com>
Date: Fri, 13 Jun 2025 14:11:33 +0100
From: Lee Jones <lee@...nel.org>
To: Ming Yu <a0282524688@...il.com>
Cc: linus.walleij@...aro.org, brgl@...ev.pl, andi.shyti@...nel.org,
	mkl@...gutronix.de, mailhol.vincent@...adoo.fr,
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, wim@...ux-watchdog.org,
	linux@...ck-us.net, jdelvare@...e.com,
	alexandre.belloni@...tlin.com, linux-kernel@...r.kernel.org,
	linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-can@...r.kernel.org, netdev@...r.kernel.org,
	linux-watchdog@...r.kernel.org, linux-hwmon@...r.kernel.org,
	linux-rtc@...r.kernel.org, linux-usb@...r.kernel.org,
	Ming Yu <tmyu0@...oton.com>
Subject: Re: [PATCH v12 1/7] mfd: Add core driver for Nuvoton NCT6694

On Fri, 13 Jun 2025, Ming Yu wrote:

> Lee Jones <lee@...nel.org> 於 2025年6月12日 週四 下午11:23寫道：
> >
> > On Thu, 12 Jun 2025, Ming Yu wrote:
> >
> > > Dear Lee,
> > >
> > > Thank you for reviewing,
> > >
> > > Lee Jones <lee@...nel.org> 於 2025年6月12日 週四 下午10:00寫道：
> > > >
> > > ...
> > > > > +static const struct mfd_cell nct6694_devs[] = {
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 0),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 1),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 2),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 3),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 4),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 5),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 6),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 7),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 8),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 9),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 10),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 11),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 12),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 13),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 14),
> > > > > +     MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 15),
> > > > > +
> > > > > +     MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 0),
> > > > > +     MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 1),
> > > > > +     MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 2),
> > > > > +     MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 3),
> > > > > +     MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 4),
> > > > > +     MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 5),
> > > >
> > > > Why have we gone back to this silly numbering scheme?
> > > >
> > > > What happened to using IDA in the child driver?
> > > >
> > >
> > > In a previous version, I tried to maintain a static IDA in each
> > > sub-driver. However, I didn’t consider the case where multiple NCT6694
> > > devices are bound to the same driver — in that case, the IDs are not
> > > fixed and become unusable for my purpose.
> >
> > Not sure I understand.
> >
> 
> As far as I know, if I maintain the IDA in the sub-drivers and use
> multiple MFD_CELL_NAME("nct6694-gpio") entries in the MFD, the first
> NCT6694 device bound to the GPIO driver will receive IDs 0~15.
> However, when a second NCT6694 device is connected to the system, it
> will receive IDs 16~31.
> Because of this behavior, I switched back to using platform_device->id.

Each of the devices will probe once.

The first one will be given 0, the second will be given 1, etc.

Why would you give multiple IDs to a single device bound to a driver?

-- 
Lee Jones [李琼斯]