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Re: [Qemu-arm] [PATCH] pl011: do not put into fifo before enabled the in

From: Peter Maydell
Subject: Re: [Qemu-arm] [PATCH] pl011: do not put into fifo before enabled the interruption
Date: Fri, 26 Jan 2018 18:01:33 +0000

On 26 January 2018 at 17:33, Wei Xu <address@hidden> wrote:
> On 2018/1/26 17:15, Peter Maydell wrote:
>> The pl011 code should call qemu_set_irq(..., 1) when the
>> guest enables interrupts on the device by writing to the int_enabled
>> (UARTIMSC) register. That will be a 0-to-1 level change and the KVM
>> VGIC should report the interrupt to the guest.
> Yes.
> And in the pl011_update, the irq level is set by s->int_level & 
> s->int_enabled.
> When writing to the int_enabled, not sure why the int_level is set to
> 0x20(PL011_INT_TX) but int_enabled is 0x50.
> It still call qemu_set_irq(..., 0).
> I added "s->int_level |= PL011_INT_RX" before calling pl011_update
> when writing to the int_enabled and tested it also works.

No, that's not right either. int_level should already have the
RX bit set, because pl011_put_fifo() sets that bit when it gets a
character from QEMU and puts it into the FIFO.

Does something else clear the int_level between the character
going into the FIFO from QEMU and the guest enabling

-- PMM

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