linux-kernel - Re: [PATCH] usb: ohci/uhci - add soft dependencies on ehci

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Message-ID: <Pine.LNX.4.44L0.1309101250220.1075-100000@iolanthe.rowland.org>
Date:	Tue, 10 Sep 2013 13:02:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tom Gundersen <teg@...m.no>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	<linux-modules@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: ohci/uhci - add soft dependencies on ehci_hcd

On Tue, 10 Sep 2013, Tom Gundersen wrote:

> Support for specifying soft dependencies in the modules themselves was
> introduced in commit 7cb14ba.
> 
> In Arch we have always been shipping a module.d(5) fragment ordering ohci/uhci
> after ehci. If this ordering is really necessary, it would be great to move it
> to the kernel and getting the correct fragment generated by depmod.

The ordering is more of a recommendation than a necessity.  Systems
should work oksy if the modules are loaded in the wrong order.

The only issue if the drivers are loaded in the wrong order is that 
full- and low-speed devices will end up being detected and enumerated 
twice, with a disconnection in between.  This can result in 
disconcerting messages appearing in the system log.

In theory, it is possible for a problem to arise.  For example, suppose
a full-speed flash drive is plugged in when the system starts up.  
When uhci-hcd or ohci-hcd gets loaded, the drive will be detected and
it may even be mounted.  Then when ehci-hcd loads, the drive will get
disconnected and reconnected.  Any open file references to the original
mount will be orphaned.

> Signed-off-by: Tom Gundersen <teg@...m.no>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/usb/host/ohci-hcd.c | 1 +
>  drivers/usb/host/uhci-hcd.c | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
> index 8f6b695..783b50a 100644
> --- a/drivers/usb/host/ohci-hcd.c
> +++ b/drivers/usb/host/ohci-hcd.c
> @@ -1171,6 +1171,7 @@ EXPORT_SYMBOL_GPL(ohci_init_driver);
>  MODULE_AUTHOR (DRIVER_AUTHOR);
>  MODULE_DESCRIPTION(DRIVER_DESC);
>  MODULE_LICENSE ("GPL");
> +MODULE_SOFTDEP("pre: ehci_hcd");
>  
>  #if defined(CONFIG_ARCH_SA1100) && defined(CONFIG_SA1111)
>  #include "ohci-sa1111.c"
> diff --git a/drivers/usb/host/uhci-hcd.c b/drivers/usb/host/uhci-hcd.c
> index 4a86b63..c2babf3 100644
> --- a/drivers/usb/host/uhci-hcd.c
> +++ b/drivers/usb/host/uhci-hcd.c
> @@ -937,3 +937,4 @@ module_exit(uhci_hcd_cleanup);
>  MODULE_AUTHOR(DRIVER_AUTHOR);
>  MODULE_DESCRIPTION(DRIVER_DESC);
>  MODULE_LICENSE("GPL");
> +MODULE_SOFTDEP("pre: ehci_hcd");

Where is MODULE_SOFTDEP defined?  It isn't mentioned in any .h files in 
my kernel tree.

Alan Stern

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