Re: sd_mod or usb-storage fails to read a single good block (was: ehci_hcd fails to read a single good block)

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Sat, 31 Mar 2012, Norman Diamond wrote:

> >> bcdDevice is 1.00
> >
> > That's the same as a bridge that was reported non-working.  Which means 
> > the OS has no way to tell them apart.
> 
> There's still something wrong here.  When the bridge is connected to Windows 
> XP, Windows accesses the correct number of blocks.  We need to find someone 
> who has a non-working but indistinguishable bridge, ask them to connect it 
> to Windows XP, and see if Windows XP gets a number of blocks that is too 
> large by 1.

How would you tell?  And what's so special about XP?  Why not Vista or 
Windows 7?

> > There is no good solution to this problem.
> 
> Agreed.  But in my case I think I need to disable that quirk entirely for 
> all USB bridges, so that my uses of Linux will always believe what the USB 
> bridge reports.  At least then my program will work correctly when working 
> bridges are attached.  Then if a user complains, we can tell them to use a 
> different bridge. 

Well, if you want to disable the quirk entirely, it's not hard to do.  
In drivers/usb/storage/scsiglue.c, just get rid of the lines that set 
sdev->fix_capacity and sdev->guess_capacity.

If you want to find out who reported the problems with the bridge chip, 
look in the unusual_devs.h file for the entry with vendor ID 0x067b and 
product ID 0x2507.

Alan Stern

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