--- "Yates, John" <jpy@xxxxxxxxxx> 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. Hmm, that sounds suspicuous. I would guess the ll/sc is just a symptom you're seeing, but that's probably not the root of the problem. If you disable ll/sc, the kernel has to emulate those instructions, if your userland code uses them, which changes the characteristics of the system, including timings. There's probably a timing problem somewhere, but ... that's just a guess. Pete > 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 > >
