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RE: Hi-Speed USB controller and au1500

To: "'Eric DeVolder'" <eric.devolder@amd.com>, linux-mips@linux-mips.org
Subject: RE: Hi-Speed USB controller and au1500
From: "Yates, John" <jpy@sparta.com>
Date: Fri, 22 Oct 2004 10:15:50 -0400
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
Thank you. This indeed works. 

The CONFIG_NONCOHERENT_IO option is set by default in config-shared.in when
one selects the db1500 board (among others). Does anyone have
recommendations as to how to modify config-shared.in to give others the
option of disabling this default behavior?

Possible places could be:

1. Add an override defaults sub-menu for the boards that support disabling
CONFIG_NONCOHERENT_IO.

2. Add a CONFIG_NONCOHERENT_IO item to the bottom of "Machine Selection"
menu. (There is already a "High Memory Support" option at the bottom of the
"machine Selection" menu.)

3. Add a CONFIG_NONCOHERENT_IO item to the "Override CPU options" sub-menu
(in the "CPU Selection" menu). 

4....

Thanks, John

-----Original Message-----
From: Eric DeVolder [mailto:eric.devolder@amd.com] 
Sent: Monday, October 18, 2004 12:28 PM
To: Yates, John
Subject: Re: Hi-Speed USB controller and au1500

I'm guessing that CONFIG_NONCOHERENT_IO is set which means that the 
buffers used by USB are non-cached, and so the LL/SC combinations 
performed by the USB stack to the structs in this non-cached area will 
always fail. (Examine the MIPS LL/SC...only works to cached spaces...)

Depending upon which version of the Au1500 you have, 
CONFIG_NONCOHERENT_IO was necessary due to coherency bugs. I believe 
everything should be fixed with Au1500 AD so that CONFIG_NONCOHERENT_IO 
isn't needed....

Eric

Yates, John wrote:

>Hello all,
>
>I am having a problem using a PCI USB 2.0 Hi-Speed controller (EHCI) with
>the dbau1500 eval kit with kernel 2.4.26. I have traced the problem down to
>a call to atomic_add() (in include/asm-mips/atomic.h) that uses assembly to
>access ll/sc registers of the mips architecture.  If I override CPU options
>and disable ll/sc when configuring the kernel,  everything works fine.
>However this causes the atomic_add() to use
>local_irq_save()/local_irq_restore().  I am assuming this will cause quite
a
>performance hit since atomic_add() gets called all over the place.  I
should
>include that the ll/sc version of atomic_add() seems to work fine until the
>call from the usb infrastructure. 
>
>Below is a code trail that leads to the call to atomic_add():
>
> 
>hub.c:                 usb_hub_port_connect_change()
>usb.c:                         usb_set_address()
>usb.c:                         usb_control_msg()
>usb.c:                         usb_internal_control_msg()
>usb.c:                         usb_start_wait_urb()
>usb.c:                         usb_submit_urb()
>usb.c:                         submit_urb()
>hcd.c:                         hcd_submit_urb()        
>host/ehci-hcd.c:               ehci_urb_enqueue()      (urb_enqueue
>function ptr)
>host/ehci-q.c:                 submit_async()  
>host/ehci-q.c:                 qh_append_tds()
>host/ehci-mem.c:               qh_get()
>atomic.h                       atomic_inc()
>atomic.h                       #define atomic_inc(v) atomic_add(1,(v)) <-
>uses ll/sc
>
>To reproduce my results:
>
>Plug in a Hi-Speed USB 2.0 controller into your pci slot and boot with a
usb
>ehci enabled  kernel. Be sure to disable the non-pci usb host that is
>built-in to the au1500 when building the  kernel. (I have tried two
>controllers (NEC and ALi) with identical results.) 
>
>Plug a Hi-Speed device (thumb drive or external HD) into the controller.
>(system stops responding here)
>
>Low/Full speed devices work without a problem because they use the ohci or
>uhci drivers. 
>
>
>Any help or direction will be greatly appreciated.
>
>John
>
>
>  
>


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