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

[Wei Xu]

Hi Andrew,

On 2018/1/29 10:29, Andrew Jones wrote:
> On Fri, Jan 26, 2018 at 06:01:33PM +0000, 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?
> 
> As part of the boot process Linux restarts the UART a few times. When
> Linux drives the PL011 with the SBSA driver then the FIFO doesn't get
> reset prior to being used again, as the SBSA doesn't specify a way to
> do that. I'm not sure if this issue is due to the SBSA attempting to
> be overly simple, or something the Linux driver can deal with. See
> this thread for a discussion I started once.
> 
> https://www.spinics.net/lists/linux-serial/msg23163.html

I am not sure it is the same problem or not.
I will check that.
Thanks!

> 
> Wei,
> 
> I assume you're using UEFI/ACPI when booting, as I don't recall this
> problem occurring with the Linux PL011 driver which would be used
> when booting with DT.
>

I am using an ARM64 board, the guest is booted *without* UEFI but the
host is booted with UEFI/ACPI.
The command I am using is as below:
        "qemu-system-aarch64 -enable-kvm -m 1024 -cpu host -M virt \
        -nographic --kernel Image --initrd roofs.cpio.gz"

Thanks!

Best Regards,
Wei

> Thanks,
> drew
> 
> .
>