Re: [PATCH 1/2] HISI LPC: Reference static MFD cells for ACPI support

[John Garry]

On 04/05/2018 11:03, Lee Jones wrote:
> On Fri, 04 May 2018, John Garry wrote:
>
> > On 04/05/2018 10:02, Lee Jones wrote:
> > > On Thu, 03 May 2018, Andy Shevchenko wrote:
> > >
> > > > On Thu, 2018-05-03 at 23:08 +0800, John Garry wrote:
> > > > > Currently for ACPI support the driver models the host as
> > > > > an MFD. For a device connected to the LPC bus, we dynamically
> > > > > create an MFD cell for that device, configuring the cell
> > > > > name and ACPI match parameters manually. This makes supporting
> > > > > named devices and also special setup handling for certain devices
> > > > > awkward, as we would need to introduce some special ACPI device
> > > > > handling according to device HID.
> > > > >
> > > > > To avoid this, create reference static MFD cells for known
> > > > > child devices, so when adding an MFD cell we can fix the cell
> > > > > platform data as required. For this, a setup callback function
> > > > > is added.
> > > > >
> > > > > For now, only the IPMI cell is added.
> > > >
> > > > > +static const struct mfd_cell *hisi_lpc_acpi_mfd_get_cell(const char
> > > > > *hid)
> > > > > +{
> > > > > +	const struct hisi_lpc_acpi_mfd_cell *cell =
> > > > > hisi_lpc_acpi_mfd_cells;
> > > > > +
> > > > > +	for (; cell && cell->mfd_cell.name; cell++) {
> > > > > +		const struct mfd_cell *mfd_cell = &cell->mfd_cell;
> > > > > +		const struct mfd_cell_acpi_match *acpi_match;
> > > > > +
> > > > > +		acpi_match = mfd_cell->acpi_match;
> > > > > +		if (!strcmp(acpi_match->pnpid, hid))
> > > > > +			return mfd_cell;
> > > > > +	}
> > > > > +
> > > > > +	return NULL;
> > > > > +}
> > > >
> > > > I'm not sure I understand why MFD core can't do it (as seen in lines
> > > > drivers/mfd/core.c:105 and below).
> >
> > Hi Lee,
> >
> > > You shouldn't be using the MFD API outside of MFD anyway.  Either it
> > > is an MFD driver, or it isn't.  If it is, please move it. If it's not,
> > > please don't use the API.
> >
> > We're modelling as an MFD, but it's not an MFD in the classic sense. We're
> > just using the MFD API for convenience (and to avoid code duplication), as
> > the MFD API does what we require for this driver.
>
> I know what you're doing, and it's wrong. ;)
>
> > > My current suspicion is that the driver needs splitting and only part
> > > of it ends up in MFD.
> >
> > How would you propose splitting the driver? By adding a lib function
> > specific for this driver for the ACPI probe?
>
> Look at:
>
>   drivers/platform/chrome/cros_ec_lpc.c
>
> and
>
>   drivers/mfd/cros_ec.c

Right, I see, something similar to what I suggested.

I don't really see a point in splitting the driver across drivers/mfd 
and drivers/bus, and introducing dependencies. This is more especially 
considering this is a legacy host controller with no potential future 
developments, and not worth the effort.

If you feel strongly enough about not using the MFD API outside 
drivers/mfd, then I'll look at other solutions, like using platform 
device APIs directly.

Cheers,
John