linux-kernel - Re: [RFC PATCH 5/9] mfd: Add ACPI support

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Date:	Thu, 28 Aug 2014 14:45:33 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Darren Hart <dvhart@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Max Eliaser <max.eliaser@...el.com>,
	linux-acpi@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/9] mfd: Add ACPI support

On Thu, Aug 28, 2014 at 12:29:00PM +0100, Lee Jones wrote:
> On Sun, 17 Aug 2014, Mika Westerberg wrote:
> 
> > If an MFD device is backed by ACPI namespace, we should allow subdevice
> > drivers to access their corresponding ACPI companion devices through normal
> > means (e.g using ACPI_COMPANION()).
> > 
> > This patch adds such support to the MFD core. If the MFD parent device
> > doesn't specify any ACPI _HID/_CID for the child device, the child device
> > will share the parent ACPI companion device. Otherwise the child device
> > will be assigned with the corresponding ACPI companion, if found in the
> > namespace below the parent.
> > 
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > Reviewed-by: Darren Hart <dvhart@...ux.intel.com>
> > ---
> >  Documentation/acpi/enumeration.txt | 27 +++++++++++++++++++++++++
> >  drivers/mfd/mfd-core.c             | 41 ++++++++++++++++++++++++++++++++++++++
> >  include/linux/mfd/core.h           |  3 +++
> >  3 files changed, 71 insertions(+)
> > 
> > diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt
> > index e182be5e3c83..74e35c54febf 100644
> > --- a/Documentation/acpi/enumeration.txt
> > +++ b/Documentation/acpi/enumeration.txt
> > @@ -312,3 +312,30 @@ a code like this:
> >  
> >  There are also devm_* versions of these functions which release the
> >  descriptors once the device is released.
> > +
> > +MFD devices
> > +~~~~~~~~~~~
> > +The MFD devices create platform devices from their children. For the
> > +child devices there needs to be an ACPI handle that they can use to
> > +reference parts of the ACPI namespace that relate to them. In the Linux
> > +MFD subsystem we provide two ways:
> > +
> > +	o The children share the parent ACPI handle.
> > +	o The MFD cell can specify the ACPI id of the device.
> > +
> > +For the first case, the MFD drivers do not need to do anything. The
> > +resulting child platform device will have its ACPI_COMPANION() set to point
> > +to the parent device.
> > +
> > +If the ACPI namespace has a device that we can match using an ACPI id,
> > +the id should be set like:
> > +
> > +	static struct mfd_cell my_subdevice_cell = {
> > +		.name = "my_subdevice",
> > +		/* set the resources relative to the parent */
> > +		.acpi_pnpid = "XYZ0001",
> > +	};
> > +
> > +The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under
> > +the MFD device and if found, that ACPI companion device is bound to the
> > +resulting child platform device.
> > diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> > index 892d343193ad..bb466b28b3b6 100644
> > --- a/drivers/mfd/mfd-core.c
> > +++ b/drivers/mfd/mfd-core.c
> > @@ -78,6 +78,45 @@ static int mfd_platform_add_cell(struct platform_device *pdev,
> >  	return 0;
> >  }
> >  
> > +#if IS_ENABLED(CONFIG_ACPI)
> > +static void mfd_acpi_add_device(const struct mfd_cell *cell,
> > +				struct platform_device *pdev)
> > +{
> > +	struct acpi_device *parent_adev;
> > +	struct acpi_device *adev = NULL;
> > +
> > +	parent_adev = ACPI_COMPANION(pdev->dev.parent);
> > +	if (!parent_adev)
> > +		return;
> > +
> > +	/*
> > +	 * MFD child device gets its ACPI handle either from the ACPI
> > +	 * device directly under the parent that matches the acpi_pnpid or
> > +	 * it will use the parent handle if is no acpi_pnpid is given.
> > +	 */
> > +	if (cell->acpi_pnpid) {
> > +		struct acpi_device_id ids[2] = {};
> > +		struct acpi_device *child_adev;
> > +
> > +		strlcpy(ids[0].id, cell->acpi_pnpid, sizeof(ids[0].id));
> > +		list_for_each_entry(child_adev, &parent_adev->children, node)
> > +			if (acpi_match_device_ids(child_adev, ids)) {
> > +				adev = child_adev;
> > +				break;
> > +			}
> 
> What happens if cell->acpi_pnpid is provided, but not matched?
> 
> Surely adev will them be NULL?
> 
> In these cases shouldn't you then "adev = parent_adev"?

Good point. I'll fix that in the next version.

> 
> > +	} else {
> > +		adev = parent_adev;
> > +	}
> > +
> > +	ACPI_COMPANION_SET(&pdev->dev, adev);
> > +}
> > +#else
> > +static inline void mfd_acpi_add_device(const struct mfd_cell *cell,
> > +				       struct platform_device *pdev)
> > +{
> > +}
> > +#endif
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