Re: sbsa_uart domU baremetal driver

[Julien Grall <julien@xxxxxxx>]

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 console

> There I expect to see my output, but nothing. Also `xl dmesg` doesn't
> show useful information.
> Any ideas?
>
> Thanks,
> Angelo
--
Julien Grall