Re: [Xen-devel] Problems after enabling rcv/xmit interrupts of ns16550 on OMAP5

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-07-17 at 17:01 +0800, Chen Baozi wrote:
> On Jul 17, 2013, at 4:21 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> 
> > On Wed, 2013-07-17 at 16:02 +0800, Chen Baozi wrote:
> >> On Jul 12, 2013, at 3:41 PM, Chen Baozi <baozich@xxxxxxxxx> wrote:
> >> 
> >>> This means you have neither registered the irq nor enabled the 
> >>> interrupts. If I turned both of these two blocks into:
> >>> 
> >>>   if ( uart->dt_irq.irq > )
> >>>   {
> >>>       ...
> >>>   }
> >>> 
> >>> There is the same phenomenon that I described in previous email. And If I 
> >>> comment either of these two blocks in my patch, my implementation works.
> >>> 
> >>> Any ideas?
> > 
> > Sorry for not replying to this, the answer was going to be "no, but I'll
> > see if I can reproduce" -- but I never got a chance.
> > 
> >> I inserted some codes in ns16550_setup_postirq to see what would cause
> >> the stuck. It seems that it will stuck while restoring CPSR or "cpsie
> >> i". But I'm not sure that these two cases are the only factors that
> >> will lead the phenomenons.
> > 
> > Does it get stuck or does it just immediately take another interrupt?
> 
> No idea. It seems the UART's receive interrupt works well, because pressing 
> "d" in the serial console could trigger dumping registers as normal. I'm 
> going into these possibilities and trying to make it sure.
> 
> > (Could indicate a level vs. edge misconfiguration perhaps?)
> > 
> > Is "restoring CPSR" this from arm32/entry.S:
> >        ENTRY(return_to_hypervisor)
> >                cpsid i
> >                ldr lr, [sp, #UREGS_lr]
> >                ldr r11, [sp, #UREGS_pc]
> >                msr ELR_hyp, r11
> >                ldr r11, [sp, #UREGS_cpsr]
> >                msr SPSR_hyp, r11
> >                pop {r0-r12}
> >                add sp, #(UREGS_SP_usr - UREGS_sp); /* SP, LR, SPSR, PC */
> >                eret
> > or elsewhere? If it is this one does changing SPSR_hyp into SPSR_cxsf 
> > change anything?
> > 
> > The "cpsie i" is from the call to local_irq_enable in gic_interrupt() or
> 
> "restoring CPSR" refers to the instruction "msr CPSR_c, <reg>" which
> is from "local_irq_restore". And "cpsie i" is from the call to
> local_irq_enable".

Ah right. So in both cases you will immediately take any pending
interrupt. I think I would continue instrumenting starting from
gic_interrupt() and hopefully eventually into the ns16550 interrupt
handler.

> 
> > somewhere else?
> > 
> > Ian.
> > 
> 



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