Re: sbsa_uart domU baremetal driver

[Julien Grall <julien@xxxxxxx>]

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>".
Best regards,

--
Julien Grall