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

[John Garry]

On 03/05/2018 17:54, 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.

Hi Andy,

> > 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).

Right, I think MFD core does the same.

> > +	/* allocate the mfd cells, one per child */
> > +	size = sizeof(*mfd_cells);
> >  	mfd_cells = devm_kcalloc(hostdev, cell_num, size,
> > GFP_KERNEL);
> >  	if (!mfd_cells)
> >  		return -ENOMEM;
>
> And since you have structures already, I'm not sure why you need another
> allocation for them. Only what you would need is to apply resources and
> call devm_mfd_add_devices() per each found device.

I was creating a copy as the originals are in the hisi_lpc_acpi_mfd_cell 
struct type, while we would require an array of mfd_cells.

> > +		cell = container_of(mfd_cell_ref, typeof(*cell),
> > mfd_cell);
>
> Why we can't iterate over inherited type of objects directly?

We could do.

Thanks,
John