Subject: Re: Test Patch: 2.5.69 Interrupt Latency
From: Paul Fulghum <paulkf@microgate.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       johannes@erdfelt.com,
       USB development list <linux-usb-devel@lists.sourceforge.net>
In-Reply-To: <Pine.LNX.4.44L0.0305161045270.738-100000@ida.rowland.org>
References: <Pine.LNX.4.44L0.0305161045270.738-100000@ida.rowland.org>
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Date: 16 May 2003 13:10:15 -0500
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On Fri, 2003-05-16 at 10:33, Alan Stern wrote:
> Paul:
> 
> On 15 May 2003, Paul Fulghum wrote:
> > Con: you would be generating a lot of spurious interrupts
> > as the global USBSTS_RD is set (incorrectly) by the OC ports.
> > Even though you would not actually do the wake, you still
> > burn cycles servicing the false interrupts.
> 
> I'm not sure about that.  For ports in a permanent OC state, the RD bit 
> would get set just once, so a single interrupt would be generated.  When 
> the host clears the Resume Detect bit in the USBSTS register, it shouldn't 
> get set again (not until a different port signals a resume).  Otherwise a 
> properly working system would generate continuous interrupts during the 
> global resume sequence.

Your interpretation checks out. The global RD interrupt does not
reoccur once the individual RD bit is set. So we get a max of
once extra interrupt per OC port.

-- 
Paul Fulghum
paulkf@microgate.com

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