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

Ming Yu
2025-06-13T01:55:09Z

Lee Jones <lee@kernel.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@kernel.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.

> > I’ve since realized that using pdev->id avoids the need for cell->id,
> > so I reverted to the earlier approach.
> >
> > That said, do you think it would be a better solution to manage all
> > the IDAs centrally within the driver? For example:
> > in nct6694.c
> > struct nct6694 {
> > struct device *dev;
> >
> > struct ida gpio_ida;
> > struct ida i2c_ida;
> > struct ida can_ida;
> > struct ida wdt_ida;
> > };
> >
> > static int nct6694_probe(struct platform_device *pdev)
> > {
> > ida_init(&nct6694->gpio_ida);
> > ...
> > }
> >
> > in gpio-nct6694.c
> > static int nct6694_gpio_probe(struct platform_device *pdev)
> > {
> > id = ida_alloc(&nct6694->gpio_ida, GFP_KERNEL);
> > }
>
> No that would be way worse.
>

Thanks,
Ming