Re: devicetree-discuss Digest, Vol 6, Issue 7

On Thu, Dec 18, 2008 at 7:17 AM, Christian Rund
[off-list ref] wrote:

From: "Grant Likely" <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>

quoted

Is a new OpenFirmware driver interface being defined for working with
'be' devices?

No

quoted

If not then the device-type property should not be
defined.

The device-type property instances will be removed where not
necessary or no OpenFirmware binding recommendations exist
respectively.

Okay, good.

quoted

quoted

Default value is { 0x00510000 0x00001000 0x00511000 0x00001000 }.

These spaces are contiguous; what is the reason for the two array entries?

The spaces are in fact contiguous, but belong to two different units.
0x00510xxx covers the IOC Address Translation MMIO Registers, whereras
0x00511xxx covers the I/O Command MMIO Registers.
Despite, Linux is mapping the two ranges in one single step, which means
the range can well be summarized to
        Default value is { 0x00510000 0x00002000 }.

Belonging to different units is not a problem if it makes logical
sense.  How Linux is currently using the data is irrelevant.  Do
whatever describes the hardware best, *but* if two ranges are used,
then the documentation must say what each of the ranges are.

quoted

quoted

The pervasive node node represents the  pervasive unit in the device
tree.
T>he main property value is the address range of MMIO register space
controlling the pervasive unit.

Umm, what is a "pervasive unit"?

The pervasive node represents the 'Pervasive MMIO Registers' (i.e.
Pervasive Monitor, Power Management and Thermal Management described
in the Cell/B.E. public register spec.

Sounds like this blurb should be added to the document.  :-)

quoted

quoted

property name: Property to specify the physical id of an SPE.

Default values for the physical id is encoded as with encode-int.

Unless there is some shared register set that needs the SPE physical
id to operate then I encourage you not to define this property.  If it
is just a logical number, the I think it is better to rely on the node
name instead of an arbitrarily defined logical number.  However, if
there is a register set shared between the SPEs that needs the SPE
number, then you should follow the lead of other existing bindings and
use the property name "cell-index" instead of physical-id.

The "physical-id" property is used by Linux (see information on ppc-patch
below).

"Because Linux Uses It" isn't actually a good answer.  The device tree
must describe the hardware platform; not the way the OS uses it.  What
is the physical ID used for?  Does it have a bearing on how Linux
drives the hardware or is it just a convenient number to uniquely id
the SPE?  If it doesn't have a bearing on how to use the hardware then
I think the 'physical-id' property is just a hack and should be
removed.  If Linux wants a unique id, then Linux should assign and
manage the ID numbers itself (IMNSHO).

If it *does* have a bearing on how to drive the hardware, then yes it
makes sense to use such a property.

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.