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

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Message-ID: <20180504100359.GD3928@dell>
Date:   Fri, 4 May 2018 11:03:59 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     John Garry <john.garry@...wei.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        xuwei5@...wei.com, mika.westerberg@...ux.intel.com,
        rjw@...ysocki.net, linux-kernel@...r.kernel.org, arnd@...db.de,
        graeme.gregory@...aro.org, helgaas@...nel.org,
        z.liuxinliang@...ilicon.com, linuxarm@...wei.com
Subject: Re: [PATCH 1/2] HISI LPC: Reference static MFD cells for ACPI support

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

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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