linux-kernel - Re: Linux 3.8-rc1 - another regression on USB :-(

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Date:	Wed, 16 Jan 2013 10:00:47 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Woody Suwalski <terraluna977@...il.com>
cc:	Andreas Mohr <andi@...as.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 3.8-rc1 - another regression on USB :-(

On Tue, 15 Jan 2013, Woody Suwalski wrote:

> > Another important change is that the EHCI driver is now split into two
> > modules.  That can slow down loading and affect the timing.
> >
> > Alan Stern
> >
> My testcase is a live initramfs + squash root.
> The boot logic is as stable as can be - unchanged since 2.6.2x kernels.
> And it was working fine till 3.8-rc1.
> 
> The modules are insmoded in a fixed order:
> usb-common, usbcore, xhci-hcd, ehci-hcd, uhci-hcd, ohci-hcd, usbhid, 
> usb_storage,...

But apparently you don't insmod ehci-pci.  That could cause problems, 
if your EHCI controller is PCI-based.

> If all USB is built as modules - I get read errors from USB drives when 
> accessing squash image, boot fails.

What read errors?  What is the cause of these errors?

> If usb-common and usbcore are built in, system seems to crawl with a 
> very slow USB, but boots. That could be caused by timing between hcd 
> modules.

Do have a dmesg log with timestamps so we can see where things go slow?  
I suggest enabling CONFIG_PRINTK_TIME and CONFIG_USB_DEBUG.  You might
even want CONFIG_USB_STORAGE_DEBUG, although that often logs too much
information.

> If usb-common, usbcore and ehci-hcd are built-in, all works OK like 
> "before 3.8".

What about ehci-pci?

> I was testing on machines  without xhci or ohci hardware, so these 
> drivers probably are not playing any role.
> I have retried initramfs with a 1s sleep between insmods to verify if it 
> is timing - still the same read errors - so the main issue is _not_ timing.
> The read errors problem is 100% reproducible for me, the blocks where 
> read fails are not fixed - every (failed) boot errors start appearing in 
> a bit different location.
> Just selecting a differently - configured  kernel image makes the boot 
> work, so it is not a problem of squash image, USB drive, squashfs driver.

Without knowing what these read errors are, it's hard to say anything 
about them.

Alan Stern

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