linux-kernel - Re: [linux-usb-devel] [PATCH] : Allow embedded developers USB options normally reserved for OTG

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Date:	Thu, 3 Jan 2008 20:20:47 -0500
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Richard D" <richard@...unus.com>
Cc:	"Bryan Wu" <cooloney.lkml@...il.com>,
	"David Brownell" <david-b@...bell.net>,
	linux-usb-devel@...ts.sourceforge.net, gregkh@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-usb-devel] [PATCH] : Allow embedded developers USB options normally reserved for OTG

On Thu 3 Jan 2008 12:04, Richard D pondered:
> Does all USB Host controller hardware have the ability to disable PING?

I think they do. (or at least should)...

http://www.intel.com/technology/usb/download/ehci-r10.pdf
==================
4.11 Ping Control (page 88)

USB 2.0 defines an addition to the protocol for high-speed devices called 
Ping. Ping is required for all USB 2.0 High-speed bulk and control endpoints. 
Ping is not allowed for a split-transaction stream. This extension to the 
protocol eliminates the bad side-effects of Naking OUT endpoints. The Status 
field has a Ping State bit, which the host controller uses to determine the 
next actual PID it will use in the next transaction to the endpoint (see 
Table 3-16).

Table 4–12 illustrates the state transition table for the host controller's 
responsibility for maintaining the PING protocol. 

Refer to Chapter 8 in the USB Specification Revision 2.0 for detailed 
description on the Ping protocol.

===============

I think the musb is just missing the PING/OUT State table, as described in 
table 4-12.

I think this is controlled in the ehci driver with:

host/ehci.h:#define     QTD_STS_PING    (1 << 0)        /* issue PING? */

-Robin
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