Re: [Qemu-devel] [PATCH] hw/arm/virt: fix pl011 and pl031 irq flags

[Christoffer Dall <christoffer.dall@linaro.org>]

On Tue, Sep 09, 2014 at 03:53:43PM +0100, Peter Maydell wrote:
> The pl011 and pl031 devices both use level triggered interrupts,
> but the device tree we construct was incorrectly telling the
> kernel to configure the GIC to treat them as edge triggered.
> This meant that output from the pl011 would hang after a while.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Cc: qemu-stable@nongnu.org
> ---
> Thanks to Christoffer Dall for figuring out the cause of the hangs here.
> 
>  hw/arm/virt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index e8f231e..1b343f0 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -371,7 +371,7 @@ static void create_uart(const VirtBoardInfo *vbi, qemu_irq *pic)
>                                       2, base, 2, size);
>      qemu_fdt_setprop_cells(vbi->fdt, nodename, "interrupts",
>                                 GIC_FDT_IRQ_TYPE_SPI, irq,
> -                               GIC_FDT_IRQ_FLAGS_EDGE_LO_HI);
> +                               GIC_FDT_IRQ_FLAGS_LEVEL_HI);
>      qemu_fdt_setprop_cells(vbi->fdt, nodename, "clocks",
>                                 vbi->clock_phandle, vbi->clock_phandle);
>      qemu_fdt_setprop(vbi->fdt, nodename, "clock-names",
> @@ -398,7 +398,7 @@ static void create_rtc(const VirtBoardInfo *vbi, qemu_irq *pic)
>                                   2, base, 2, size);
>      qemu_fdt_setprop_cells(vbi->fdt, nodename, "interrupts",
>                             GIC_FDT_IRQ_TYPE_SPI, irq,
> -                           GIC_FDT_IRQ_FLAGS_EDGE_LO_HI);
> +                           GIC_FDT_IRQ_FLAGS_LEVEL_HI);
>      qemu_fdt_setprop_cell(vbi->fdt, nodename, "clocks", vbi->clock_phandle);
>      qemu_fdt_setprop_string(vbi->fdt, nodename, "clock-names", "apb_pclk");
>      g_free(nodename);
> -- 
> 1.9.1
> 
I've been trying to figure out why we would see this particular hang
with SMP and not UP (or maybe it is just very much more unlikely to
happen with UP), but haven't been able to come up with a sequence of
events to support this yet.  It also worries me that we weren't seeing
this with KVM, since it indicates that we're either doing something
wrong in the KVM or QEMU GIC emulation code, potentially.

In any case, this patch is correct, so:

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>