Re: [Xen-devel] Xen ARM - Exposing a PL011 to the guest

[Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>]

Hi Stefano,

On 9 February 2017 at 05:40, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> On Wed, 8 Feb 2017, Bhupinder Thakur wrote:
>> Hi Julien,
>>
>> On 3 February 2017 at 19:38, Julien Grall <julien.grall@xxxxxxx> wrote:
>> > So if I understand correctly, you don't receive anymore output. Correct?
>> > Have you tried to see whether the pl011 driver is receiving interrupt or
>> > even Linux calling it.
>>
>> The pl011 driver is not receiving the interrupts (I put a
>> HYPERVISOR_console_io() call inside the interrupt handler and I do not
>> see the print on the xen console) . When the console is in this state,
>> if I keep typing the characters on the console then Xen keeps raising
>> the interrupts (for each character typed) but all those interrupts are
>> marked as inflight. So it seems that interrupt is not getting cleared
>> in GIC. Which GIC function can I look at to further debug what is the
>> issue?
>>
>> Earlier, when I used to manually write characters to /dev/ttyAMA0 then
>> I used to receive the interrupts all fine.
>
> DomU doesn't get emulated PL011 interrupts from Xen? Make sure you don't
> mark the interrupt as a real hardware interrupt by mistake
> (GICH_V2_LR_HW). At the same time, check that the virtual PL011
> interrupt has been added correctly to the LRs
> (xen/arch/arm/gic-v2.c:gicv2_update_lr).

I verified that the PL011 interrupt is getting marked pending by Xen
but guest does not receive it. I am not sure if the local interrupt
delivery is disabled on the guest because of which it may not be
receiving the interrupts. Is there a way to verify that interrupts are
indeed disabled at that point. Since the interrupt delivery works fine
when I manually read/write characters to /dev/ttyAMA0, I think there
is no issue from the Xen side in terms of raising an interrupt.

One observation is that pl011_request_port () calls request_mem_region
() for the MMIO space allocated to pl011. The function returns -EBUSY
indicating that the memory region is already in use. But when I do cat
/proc/iomem, I do not see any overlaps. I am using 0x22000000 as the
start of the pl011 MMIO space. I see the same error while booting the
dom0 kernel also.

I have attached the guest boot logs when console=ttyAMA0. I have added
debug prints marked with [DEBUG]. I added debug prints in amba-pl011.c
and serial_core.c. The output from the console seems to suddenly stop
once the pl011 port is started. I have not added getty for ttyAMA0 in
the /etc/inittab file. I believe auto-serial-console should be able to
attach a getty session to ttyAMA0 automatically (i did try with adding
a getty command in the inittab file but that did not solve the issue).

Towards the end of the log, we can see that every time a character is
typed, Xen raises an interrupt and the characters keep getting
collected in the IN RING buffer (in_prod keeps incrementing). Later
interrupts remain in inflight as the earlier interrupt is not cleared.

Regards,
Bhupinder

Attachment: pl011.log
Description: Text Data

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