PCI changes kill USB PM

From: Benjamin Herrenschmidt (benh_at_kernel.crashing.org)
Date: 10/30/04

  • Next message: James Cleverdon: "Re: [Patch] x86-64: fix sibling map again!" 
    To: Greg KH <greg@kroah.com>, David Brownell <david-b@pacbell.net>
Date:	Sat, 30 Oct 2004 10:14:04 +1000

    Hi !

    The recent PCI changes are killing USB Power Management, and maybe more.
    The problem is that the common PCI code will now always call
    pci_save_state() after calling the pci_driver->suspend().

    The USB suspend() code does pci_save_state() then pci_disable_device(),
    which clears PCI_COMMAND_MASTER in the PCI command register.

    So when later on, the PCI core calls pci_save_state() again, it saves a
    state that corresponds to a suspended device with the command register
    "disabled".

    On wakeup, USB does pci_set_mater() then pci_restore_state(). Now, what
    happen is that the later "undos" the work done by pci_set_master(),
    restoring a command register with PCI_COMMAND_MASTER clear. Bad bad bad.

    This triggers a very funny behaviour on pmac laptops btw, for some
    reason, the Apple IO ASIC that contains the 2 OHCI's along with a bunch
    of other devices like IDE gets crazy of this situation (the controller
    is enabled, tries to bus master, but isn't allowed to do so by it's
    command reg) and the whole ASIC seem to lose all sense of PCI
    arbitration, IDE throughput goes down to about 40Kb/sec for example...

    There are 2 issues here. One is that USB should definitely call
    pci_set_master() _after_ pci_resume_state(), though it shouldn't need to
    call it at all ...

    The other one is that I don't like the asymetry in the PCI core of one
    side always calling pci_save_state() after the driver suspend() while
    the other side only calls pci_restore_state() when there is no driver
    resume()... I really prefer having save_state & restore_state 100% under
    driver control when the driver has suspend & resume routines.

    This patch takes cares of both, Andrew, do not apply before Ack from
    Greg since the change in the PCI code may affect some other things (I
    hope you didn't start removing calls to pci_save_state() from
    drivers ? :)

    Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

    Index: linux-work/drivers/usb/core/hcd-pci.c
    ===================================================================
    --- linux-work.orig/drivers/usb/core/hcd-pci.c 2004-10-20 13:01:02.000000000 +1000
    +++ linux-work/drivers/usb/core/hcd-pci.c 2004-10-29 17:57:52.027929064 +1000
    @@ -366,7 +366,6 @@
                             "can't restore IRQ after resume!\n");
                     return retval;
             }
    - pci_set_master (dev);
             pci_restore_state (dev);
     #ifdef CONFIG_USB_SUSPEND
             pci_enable_wake (dev, dev->current_state, 0);
    Index: linux-work/drivers/pci/pci-driver.c
    ===================================================================
    --- linux-work.orig/drivers/pci/pci-driver.c 2004-10-20 13:01:02.000000000 +1000
    +++ linux-work/drivers/pci/pci-driver.c 2004-10-29 17:57:44.202118768 +1000
    @@ -308,8 +308,8 @@
             dev_state = state_conversion[state];
             if (drv && drv->suspend)
                     i = drv->suspend(pci_dev, dev_state);
    -
    - pci_save_state(pci_dev);
    + else
    + pci_save_state(pci_dev);
             return i;
     }
     

    -
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