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

[Wei Xu]

Hi Peter,

On 2018/1/26 18:01, Peter Maydell wrote:
> 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
> interrupts?

Yes. When the guest enabling the interrupts, the pl011 driver in
the kernel will clear the RX interrupts[1].
And pasted the code below to make it easy to read.

        static void pl011_enable_interrupts(struct uart_amba_port *uap)
        {
                spin_lock_irq(&uap->port.lock);

                /* Clear out any spuriously appearing RX interrupts */
                pl011_write(UART011_RTIS | UART011_RXIS, uap, REG_ICR);
                uap->im = UART011_RTIM;
                if (!pl011_dma_rx_running(uap))
                uap->im |= UART011_RXIM;
                pl011_write(uap->im, uap, REG_IMSC);
                spin_unlock_irq(&uap->port.lock);
        }

I tried kept the RXIS in the kernel side to test and found the issue is still 
there.
A little confused now :(

[1]: 
https://elixir.free-electrons.com/linux/latest/source/drivers/tty/serial/amba-pl011.c#L1732

Best Regards,
Wei

> 
> thanks
> -- PMM
> 
> .
>