On Thu, Jun 5, 2025 at 8:14 PM Florian Lugou
<florian.lu...@provenrun.com> wrote:
>
> The current handler for TXFIFO writes schedules an async callback to
> pop characters from the queue. When software writes to TXFIFO faster
> than the async callback delay (100ns), the timer may be pushed back
> while the previous character has not be dequeued yet. This happens in
> particular when using -icount with small shift values. This is
> especially worrysome when software repetitively issues amoor.w
> instructions (as suggested by SiFive specification) and the FIFO is
> full, leading to the callback being infinitly pushed back.
>
> This commit fixes the issue by never pushing back the timer, only
> updating it if it is not already active.
>
> Signed-off-by: Florian Lugou <florian.lu...@provenrun.com>
Thanks!
Applied to riscv-to-apply.next
Alistair
> ---
> hw/char/sifive_uart.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/hw/char/sifive_uart.c b/hw/char/sifive_uart.c
> index 0fc89e76d1..9bc697a67b 100644
> --- a/hw/char/sifive_uart.c
> +++ b/hw/char/sifive_uart.c
> @@ -128,8 +128,10 @@ static void sifive_uart_write_tx_fifo(SiFiveUARTState
> *s, const uint8_t *buf,
> s->txfifo |= SIFIVE_UART_TXFIFO_FULL;
> }
>
> - timer_mod(s->fifo_trigger_handle, current_time +
> - TX_INTERRUPT_TRIGGER_DELAY_NS);
> + if (!timer_pending(s->fifo_trigger_handle)) {
> + timer_mod(s->fifo_trigger_handle, current_time +
> + TX_INTERRUPT_TRIGGER_DELAY_NS);
> + }
> }
>
> static uint64_t
> --
> 2.43.0
>
>
