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

From: Peter Maydell <peter.maydell@linaro.org>
To: Wei Xu <xuwei5@hisilicon.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	qemu-arm <qemu-arm@nongnu.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Linuxarm <linuxarm@huawei.com>,
	Rob Herring <rob.herring@linaro.org>,
	Daode Huang <huangdaode@hisilicon.com>,
	"Chenxin (Charles)" <charles.chenxin@huawei.com>,
	Zhangyi ac <zhangyi.ac@huawei.com>,
	"Liguozhu (Kenneth)" <liguozhu@hisilicon.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	"Liuxinliang (Matthew Liu)" <z.liuxinliang@hisilicon.com>,
	tiantao6@huawei.com, Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH] pl011: do not put into fifo before enabled the interruption
Date: Fri, 26 Jan 2018 18:01:33 +0000	[thread overview]
Message-ID: <CAFEAcA-_vYgDYofx61rmCL7sZKOVSBHfw0k3us1=SHzD+TEnGw@mail.gmail.com> (raw)
In-Reply-To: <5A6B6671.8070408@hisilicon.com>

On 26 January 2018 at 17:33, Wei Xu <xuwei5@hisilicon.com> 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?

thanks
-- PMM