Re: [PATCH] usb: ohci/uhci - add soft dependencies on ehci_hcd

On Tue, 10 Sep 2013, Tom Gundersen wrote:

Hi Alan,

On Tue, Sep 10, 2013 at 7:02 PM, Alan Stern [off-list ref] wrote:

quoted

On Tue, 10 Sep 2013, Tom Gundersen wrote:

quoted

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.

Thanks for the explanation. Sounds to me that a softdep is indeed appropriate:

//
The softdep command allows you to specify soft, or optional, module
dependencies. modulename can be used without these optional modules
installed, but usually with some features missing. For example, a
driver for a storage HBA might require another module be loaded in
order to use management features.

pre-deps and post-deps modules are lists of names and/or aliases of
other modules that modprobe will attempt to install (or remove) in
order before and after the main module given in the modulename
argument.
//

So this means that before installing ohci-hcd, modprobe would attempt 
to install ehci-hcd?  And if the attempt failed, it would go ahead and 
load ohci-hcd anyway?

What about during unloading?  Would this mean that rmmod ohci-hcd would 
automatically cause ehci-hcd to be unloaded also?  Or would unloading 
ehci-hcd cause ohci-hcd to be unloaded?

quoted

quoted

Signed-off-by: Tom Gundersen <redacted>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.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.

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/linux/module.h#n104

I think I get the picture.

The MODULE_SOFTDEP lines should be moved to uhci-pci.c and ohci-pci.c,
because the ordering restrictions apply only to the PCI versions of
these drivers.  And they should specify "pre: ehci-pci", not ehci-hcd.

Alan Stern