linux-kernel - Re: [PATCH v10 1/7] mfd: Add core driver for Nuvoton NCT6694

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Message-ID: <20250509142819.GG2492385@google.com>
Date: Fri, 9 May 2025 15:28:19 +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 v10 1/7] mfd: Add core driver for Nuvoton NCT6694

On Fri, 02 May 2025, Ming Yu wrote:

> Lee Jones <lee@...nel.org> 於 2025年5月2日 週五 下午4:08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),
> > > >
> > > > These are all identical.
> > > >
> > > > I thought you were going to use PLATFORM_DEVID_AUTO?  In fact, you are
> > > > already using PLATFORM_DEVID_AUTO since you are calling
> > > > mfd_add_hotplug_devices().  So you don't need this IDs.
> > > >
> > > > MFD_CELL_NAME() should do.
> > > >
> > >
> > > Yes, it uses PLATFORM_DEVID_AUTO, but in my implementation, the
> > > sub-devices use cell->id instead of platform_device->id, so it doesn't
> > > affect the current behavior.
> > > However, if you think there's a better approach or that this should be
> > > changed for consistency or correctness, I'm happy to update it, please
> > > let me know your recommendation.
> > >
> > > When using MFD_CELL_NAME(), the platform_device->id for the GPIO
> > > devices is assigned values from 1 to 16, and for the I2C devices from
> > > 1 to 6, but I need the ID offset to start from 0 instead.
> >
> > Oh no, don't do that.  mfd_cell isn't supposed to be used outside of MFD.
> >
> > Just use the platform_device id-- if you really need to start from 0.
> >
> > As an aside, I'm surprised numbering starts from 1.
> >
> 
> OK, I will use platform_device->id instead. However, I'm still unsure
> why the ID starts from1.
> 
> Additionally, I noticed that when calling mfd_add_devices()
> separately, the IDs are also assigned consecutively (e.g., GPIO: 1~16,
> I2C: 17~22, ...).
> 
> Do you have any recommendations on how I should implement this?

If you are to use this mechanism, you'd have to submit separate
mfd_add_devices() calls I guess.

However, this all seems a bit silly for simple, contextless (where
device 3 is identical to device 10, etc) enumeration.  Can you use IDA
instead?

-- 
Lee Jones [李琼斯]