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[XenARM] [MINIOS] evtchn_pending_sel issue

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Subject: [XenARM] [MINIOS] evtchn_pending_sel issue
From: ROSSIER Daniel <Daniel.Rossier@xxxxxxxxxx>
Date: Tue, 9 Jun 2009 17:43:29 +0200
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Thread-topic: [MINIOS] evtchn_pending_sel issue
Hi Folks,
 
Can anybody help us in the following problem:
(still working on embeddedXEN with ARM core)
 
we're trying to use miniOS (basically the same than x86 version) and we face a strange issue regarding
the hypervisor callback. Here is a portion of code:
 
#define active_evtchns(cpu,sh,idx)              \
    ((sh)->evtchn_pending[idx] &                \
     ~(sh)->evtchn_mask[idx])
 
l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
        while (l1 != 0) {
                l1i = __ffs(l1);
                l1 &= ~(1 << l1i);
                while ((l2 = active_evtchns(cpu, s, l1i)) != 0) {
                        l2i = __ffs(l2);
                        l2 &= ~(1 << l2i);
 
                        port = (l1i << 5) + l2i;
                        do_event(port, regs);
                }
        }
 
The timer init function bind the VIRQ_TIMER to a specific handler, ok. VIRQ_TIMER is equal to 0 and therefore, the bit 0 of
evtchn_pending and evtchn_mask are set correctly (checked). However, the code above tells us that l1i is set to 1 (and not 0).
Consequently, we never statisfy the second while() condition.
 
It seems that there is a shift of one bit in the computation of l1i, since _ffs return 1 for the least significant bit (and not 0).
What do you think?
 
What I'm wondering is how it could work .. (and probably it could ;-) just something that probably I missed….
 
Thanks for your help
 
Daniel
 
 
 
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