Re: [Qemu-devel] Guest application reading from pl011 without device driver

[Jiahuan Zhang]

many thanks for the rapid reply!

On 21 March 2017 at 17:39, Peter Maydell <address@hidden> wrote:

> On 21 March 2017 at 16:32, Jiahuan Zhang <address@hidden> wrote:
> > I found the serial device is always trying to receive all the data when
> > ReadFile() is running, then start reading. Even if the fifo is full, the
> > _can_receive function still keeps polling if the data is larger than 16
> > bytes.
>
> pl011_can_receive() is:
>
> static int pl011_can_receive(void *opaque)
> {
>     PL011State *s = (PL011State *)opaque;
>     int r;
>
>     if (s->lcr & 0x10) {
>         r = s->read_count < 16;
>     } else {
>         r = s->read_count < 1;
>     }
>     trace_pl011_can_receive(s->lcr, s->read_count, r);
>     return r;
> }


> so if the FIFO fills up then it should start to return 'false',
> as it is supposed to.
>
> I'm not sure from your description what exactly is happening,
> but you should probably check, for instance:
>  * whether pl011_can_receive is returning false but data
>    is still being fed to it
>

The actual situation is, pl011_can_receive is returning false, the fifo is
full,
pl011_read does't start.
At this moment, only pl011_can_recieve is keeping returning 0.


>  * whether pl011_can_receive is returning true even with
>    16 bytes in the fifo (hard to see how, given the code)
>  * whether the fifo actually has fewer bytes in it because
>    the guest is reading them
>

No, because the guest application does't get any data.


>  * etc
>
> thanks
> -- PMM
>