• Mikael Pettersson's avatar
    m68k: Correct the Atari ALLOWINT definition · c6636005
    Mikael Pettersson authored
    Booting a 3.2, 3.3, or 3.4-rc4 kernel on an Atari using the
    `nfeth' ethernet device triggers a WARN_ONCE() in generic irq
    handling code on the first irq for that device:
    
    WARNING: at kernel/irq/handle.c:146 handle_irq_event_percpu+0x134/0x142()
    irq 3 handler nfeth_interrupt+0x0/0x194 enabled interrupts
    Modules linked in:
    Call Trace: [<000299b2>] warn_slowpath_common+0x48/0x6a
     [<000299c0>] warn_slowpath_common+0x56/0x6a
     [<00029a4c>] warn_slowpath_fmt+0x2a/0x32
     [<0005b34c>] handle_irq_event_percpu+0x134/0x142
     [<0005b34c>] handle_irq_event_percpu+0x134/0x142
     [<0000a584>] nfeth_interrupt+0x0/0x194
     [<001ba0a8>] schedule_preempt_disabled+0x0/0xc
     [<0005b37a>] handle_irq_event+0x20/0x2c
     [<0005add4>] generic_handle_irq+0x2c/0x3a
     [<00002ab6>] do_IRQ+0x20/0x32
     [<0000289e>] auto_irqhandler_fixup+0x4/0x6
     [<00003144>] cpu_idle+0x22/0x2e
     [<001b8a78>] printk+0x0/0x18
     [<0024d112>] start_kernel+0x37a/0x386
     [<0003021d>] __do_proc_dointvec+0xb1/0x366
     [<0003021d>] __do_proc_dointvec+0xb1/0x366
     [<0024c31e>] _sinittext+0x31e/0x9c0
    
    After invoking the irq's handler the kernel sees !irqs_disabled()
    and concludes that the handler erroneously enabled interrupts.
    
    However, debugging shows that !irqs_disabled() is true even before
    the handler is invoked, which indicates a problem in the platform
    code rather than the specific driver.
    
    The warning does not occur in 3.1 or older kernels.
    
    It turns out that the ALLOWINT definition for Atari is incorrect.
    
    The Atari definition of ALLOWINT is ~0x400, the stated purpose of
    that is to avoid taking HSYNC interrupts.  irqs_disabled() returns
    true if the 3-bit ipl & 4 is non-zero.  The nfeth interrupt runs at
    ipl 3 (it's autovector 3), but 3 & 4 is zero so irqs_disabled() is
    false, and the warning above is generated.
    
    When interrupts are explicitly disabled, ipl is set to 7.  When they
    are enabled, ipl is masked with ALLOWINT.  On Atari this will result
    in ipl = 3, which blocks interrupts at ipl 3 and below.  So how come
    nfeth interrupts at ipl 3 are received at all?  That's because ipl
    is reset to 2 by Atari-specific code in default_idle(), again with
    the stated purpose of blocking HSYNC interrupts.  This discrepancy
    means that ipl 3 can remain blocked for longer than intended.
    
    Both default_idle() and falcon_hblhandler() identify HSYNC with
    ipl 2, and the "Atari ST/.../F030 Hardware Register Listing" agrees,
    but ALLOWINT is defined as if HSYNC was ipl 3.
    
    [As an experiment I modified default_idle() to reset ipl to 3, and
    as expected that resulted in all nfeth interrupts being blocked.]
    
    The fix is simple: define ALLOWINT as ~0x500 instead.  This makes
    arch_local_irq_enable() consistent with default_idle(), and prevents
    the !irqs_disabled() problems for ipl 3 interrupts.
    
    Tested on Atari running in an Aranym VM.
    Signed-off-by: default avatarMikael Pettersson <mikpe@it.uu.se>
    Tested-by: Michael Schmitz <schmitzmic@googlemail.com> (on Falcon/CT60)
    Signed-off-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
    c6636005
entry.h 5.73 KB