Re: sbsa_uart domU baremetal driver

[Angelo Ruocco <angelo.ruocco.90@xxxxxxxxx>]

On 20/10/2020, Julien Grall <julien@xxxxxxx> wrote:
> Hi,
>
> Sorry, I pressed sent by mistake.
>
> On 20/10/2020 10:48, Julien Grall wrote:
>>
>>
>> On 14/10/2020 23:28, Angelo Ruocco wrote:
>>> Hi,
>>
>> Hello,
>>
>>>
>>> I'm trying to write a baremetal domU application on arm64 and I'm
>>> having some troubles making it print on the vpl011 serial.
>>>
>>> The application works fine if I use the UART driver of the board I'm
>>> using (XUARTPS on Xilinx ZCU104), but as soon as I try to use the
>>> virtual console, then I get no output at all. I'm using a custom pl011
>>> driver that works on other (real) consoles. I'm not trying to have it
>>> read chars, just print them, so the driver is quite simple.
>>>
>>> If I try to do something 'wrong' with the virtual UART, I have Xen
>>> complaining of unaligned access to the vpl011 driver, so Xen is able
>>> to see that I'm trying to use the console. But as soon as I correctly
>>> (I think) write to the data output region of the driver, my
>>> application writes exactly 369 characters before crashing or freezing.
>>> Note that I don't see those bytes, I just know that the `putchar`
>>> function gets called 369 times, even when I try to print more than 369
>>> characters.
>>>
>>> My understanding is that the under the hood vpl011 uses the ring
>>> buffer, which by default should be emptied at max every time it gets
>>> half-full, so I'm not sure why I'm allowed to write only 369 bytes.
>>>
>>> The memory region mapped for the uart is uncached, so it shouldn't be
>>> a problem of dirty cache.
>>>
>>> I'm afraid I'm missing something stupid, so here's my setup:
>>>
>>> Xen version 4.13
>>> on the .cfg file I have `vuart = "sbsa_uart"`
>>> I start the domU with `xl create -c baremetal.cfg`
>>
>> There are multiple console available to the guest (e.g. PV, SBSA).
>
> The option -c will open the PV console. In this case, you will want to
> use "xl console -t vuart <domain>".

Ah. Yeah, I missed that, thank you.

Still, no luck with the output, what I get from that is:

`xenconsole: Could not read tty from store: No such file or directory`

Some other trivial mistake I could be making?
Yes, `xenconsoled` and `xenstored` are running.

Thank you,
Angelo

>
> Best regards,
>
> --
> Julien Grall
>