Re: [PATCH v2 3/4] hw/char/pl011: better handling of FIFO flags on LCR reset

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 17 Jan 2023 at 22:05, Evgeny Iakovlev
<eiakovlev@linux.microsoft.com> wrote:
>
> Current FIFO handling code does not reset RXFE/RXFF flags when guest
> resets FIFO by writing to UARTLCR register, although internal FIFO state
> is reset to 0 read count. Actual guest-visible flag update will happen
> only on next data read or write attempt. As a result of that any guest
> that expects RXFE flag to be set (and RXFF to be cleared) after resetting
> FIFO will never see that happen.
>
> Signed-off-by: Evgeny Iakovlev <eiakovlev@linux.microsoft.com>
> ---
>  hw/char/pl011.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/hw/char/pl011.c b/hw/char/pl011.c
> index 404d52a3b8..3184949d69 100644
> --- a/hw/char/pl011.c
> +++ b/hw/char/pl011.c
> @@ -87,6 +87,13 @@ static inline unsigned pl011_get_fifo_depth(PL011State *s)
>      return s->lcr & 0x10 ? PL011_FIFO_DEPTH : 1;
>  }
>
> +static inline void pl011_reset_pipe(PL011State *s)
> +{
> +    s->read_count = 0;
> +    s->read_pos = 0;
> +    s->flags = PL011_FLAG_RXFE | PL011_FLAG_TXFE;

Should this really be resetting all the other flags to 0 ?
I think we should set/clear only the FIFO related flags, and
leave the others alone. We don't yet implement the
modem-status signals, but if/when we ever do, clearing them
would be the wrong thing here.

(Reset still needs to reset all the flag register bits.)

thanks
-- PMM