linux-kernel - Re: [linux-usb-devel] [PATCH] USB BIOS early handoff only when the we the driver is configured

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Message-ID: <Pine.LNX.4.44L0.0707311058470.3520-100000@iolanthe.rowland.org>
Date:	Tue, 31 Jul 2007 11:04:18 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Engraf <david.engraf@...com.eu>
cc:	linux-kernel@...r.kernel.org, <linux-pci@...ey.karlin.mff.cuni.cz>,
	<gregkh@...e.de>, <linux-usb-devel@...ts.sourceforge.net>
Subject: Re: [linux-usb-devel] [PATCH] USB BIOS early handoff only when the
 we the driver is configured

On Tue, 31 Jul 2007, David Engraf wrote:

> When CONFIG_USB_UHCI_HCD, CONFIG_USB_OHCI_HCD or CONFIG_USB_EHCI_HCD is
> not configured we don't need to call the quirk_usb_handoff_xxxx function
> in driver/usb/host/pci_quiks.c.
> 
> I think the kernel shouldn't take the control over the usb controller
> when we don't have the driver for it,
> so with this patch the kernel takes the control only when the driver is
> configured.

Have you found a system where this really improves behavior or is it 
just theoretical?

There _is_ a theoretical reason for running the handoff routines even 
when the corresponding driver isn't configured.  Namely, at startup the 
controller will be in some undetermined state as a result of usage by 
the firmware.  Resetting it to a known idle state is a good idea.

Bear in mind that on some systems, not performing the handoff has
caused interrupt storms during startup.

Alan Stern

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