Hi Rafael,

On 29 December 2011 03:47, Rafael J. Wysocki [off-list ref] wrote:

On Wednesday, December 28, 2011, Thomas Abraham wrote:

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Hi Mark, Rafael,

Hi,

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On 27 December 2011 02:14, Rafael J. Wysocki [off-list ref] wrote:

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On Monday, December 26, 2011, Mark Brown wrote:

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On Mon, Dec 26, 2011 at 08:13:19PM +0100, Rafael J. Wysocki wrote:

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On Monday, December 12, 2011, Thomas Abraham wrote:

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A device node pointer is added to generic pm domain structure to associate
the domain with a node in the device tree.

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That sounds fine except for one thing: PM domains are not devices, so adding
"device node" pointers to them is kind of confusing. ?Perhaps there should be
something like struct dt_node, representing a more general device tree node?

There's struct of_node which is exactly that, though practically
speaking you need a device if you're going to bind automatically to
something from the device tree in a sensible fashion and there is actual
hardware under there so a device does make some sense.

In patch 2/2 of this series, the platform code looks for nodes in
device tree that represent a power domain. When a power domain node is
found, a generic power domain is instantiated with pm_genpd_init()
using the information available from the node in device tree. There is
no automatic binding required in this case. The power domain node does
represent a hardware that manages the power domain.

Good. ?So would it be possible to use struct of_node instead of
struct device_node in struct generic_pm_domain?

Sorry, I used 'struct of_node' and 'struct device_node'
interchangeably in my reply. All the nodes in a device tree are
represented by 'struct device_node'.

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This is in part compatibility with the existing Exynos code which uses
devices to probe the domains for non-DT systems.

Well, that's not a general case, though.

It doesn't feel approporiate to use a "device node" pointer for something
that's not based on struct device, at least not a generic level, so I wonder
if there's a different way.

A device node pointer or of_node pointer is a simple pointer to a
instance of a node in device tree. All nodes in a device tree need not
represent a corresponding 'struct device'. A node in device tree can
described a hardware feature such as a power domain supported in the
hardware.

Sure.

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The addition of device tree support for generic power domains in this
patchset is generic for all platforms. The platform code instantiates
generic power domains from device tree with the of_node pointer
assigned to 'struct generic_pm_domain'. Then, in
__pm_genpd_add_device(), given a of_node pointer (to gen_pd), it is
possible to find a matching power domain to select.

My point was that adding the struct device_node pointer to
struct generic_pm_domain didn't look good, because that structure didn't
represent a device in general. ?While I understand that it may be regarded
as a "device object" on some platforms, there are platforms that don't
regard PM domains as devices. ?For this reason (and only for this reason)
it appears to be more appropriate to use a more generic device tree node
type for struct generic_pm_domain.

If a platform uses some hardware controls (register read/writes) to
enable/disable/control power domain, then it can be represented in the
device tree. But such a node need not represent a 'struct device'.
Other nodes in the device tree can then reference the power domain
node.

If a platform does not have any hardware knobs for controlling power
domains, then probably it will not be represented in the device tree.
But I am not sure of this case.

The 'struct device_node' is a representation of a instance of a device
tree node. It can represent nodes that are not devices. Hence, it can
be used to represent a power domain in a device tree and also included
in the 'struct generic_pm_domain'.

Thanks,
Thomas.

Thanks,
Rafael