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

[Andrew Jones]

On Mon, Jan 29, 2018 at 11:37:05AM +0000, Wei Xu wrote:
> 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"

Hmm. This means you're booting the guest with DT, which means the
Linux driver is the PL011 driver, not the SBSA driver. I didn't
recall that driver having the issue, but maybe something changed.

Thanks,
drew

> 
> Thanks!
> 
> Best Regards,
> Wei
> 
> > Thanks,
> > drew
> > 
> > .
> > 
> 
>