Date: Mon, 22 Apr 1996 23:45:49 -0700
From: jordan@pongo.West.Sun.COM (Jordan Brown)
Subject: Item #342: Device Support Extensions: Clarify Scope

P1275 Openboot Working Group Proposal -- Proposal #:342 Ver 2

Title:          Device Support Extensions: Clarify Scope

Author:         Jordan Brown

Date:           22 April 1996

Ed/Tech:        Editorial

Synopsis:       The scope of the Device Support Extensions document is vague.

Doc & Version:  Device Support Extensions (all versions)

Problem:

David Kahn correctly complains that the DSE does not make it clear that
it is an optional supplement to the core.  This proposal supplies some
words to make the scope clearer.

First, my perception of the intent of the DSE:  The DSE defines
"device_type" values in addition to those described in 1275-1994 section
3.7.  It is expected that the DSE, or parts thereof, will be specified
as "required" by platform bindings.  It is *desired* that all platform
bindings do so, in order to maximize the platform-independence of client
software.  One way to summarize the intent is that 1275-1994 section 3.7
is "version 1.0" of device support in Open Firmware, and the DSE is
"version 1.1", supplying additional definitions, clarifications, and
additional functionality.  It is not intended to _conflict_ with any
existing implementations.  Existing implementations most likely do not
provide the services described, but as long as they do not advertise the
"device_type" values described they are not in conflict.  For "scsi",
"block", and "byte", existing implementations are likely to support only
the base 1275-1994 semantics, and that's OK.  A client intended for
these environments will have to take this into account.

Proposal:       

(1) Replace the "purpose" paragraph with

	This document specifies the semantics of "device_type" values
	in addition to those specified in IEEE 1275-1994 section 3.7.
	It also specifies some additional semantics for 1275-1994 defined
	"device_type" values.  It is expected and recommended that new
	implementations comply with the specifications in this document
	and that new platform bindings call out this document as required
	for compliance.
	
(2) In section 1. "Overview", replace

	It is intended that Open Firmware implementations supporting these
	device types will supply the methods and properties described herein.

    with

	It is recommended that Open Firmware implementations supporting
	the devices described herein conform to this specification.
	This specification does not, however, require that any
	particular device be supported in the specified way.  What it
	requires is that if the device is advertised as having the
	specified device_type value, it should have the specified
	semantics.

(3) In section 9 "Additional Requirements for SCSI Devices", add

	Note:  As implementations prior to the introduction of this
	specification may use the "scsi" device_type value, clients must
	augment this information with platform-specific knowlege of
	whether these features are supported on this platform.

(4) In section 10 "Additional Requirements for Block and Byte Devices", add
    at the end:

	Note:  As implementations prior to the introduction of this
	specification may not support these methods, clients wishing to
	use these methods must either have platform-specific knowlege
	that they are present or must test for their presence.

(5) In section 11 "Additional Requirements for Block Devices", add
    at the end:

	Note:  As implementations prior to the introduction of this
	specification may not support these methods, clients wishing to
	use these methods must either have platform-specific knowlege
	that they are present or must test for their presence.


Note for discussion:  Perhaps we should define properties for "scsi",
"block", and "byte" indicating that these features are present.

[ P1275 Item #342 -- Received: Mon Apr 22 23:44:04 PDT 1996 ]