On 10/9/24 06:54, Alistair Francis wrote:
The current approach of using qemu_chr_fe_write() and ignoring the
return values results in dropped characters [1].
Let's update the SiFive UART to use a async sifive_uart_xmit() function
to transmit the characters and apply back pressure to the guest with
the SIFIVE_UART_TXFIFO_FULL status.
This should avoid dropped characters and more realisticly model the
hardware.
1: https://gitlab.com/qemu-project/qemu/-/issues/2114
Signed-off-by: Alistair Francis <alistair.fran...@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com>
Tested-by: Thomas Huth <th...@redhat.com>
---
include/hw/char/sifive_uart.h | 16 +++++-
hw/char/sifive_uart.c | 94 ++++++++++++++++++++++++++++++++---
2 files changed, 102 insertions(+), 8 deletions(-)
+static void sifive_uart_write_tx_fifo(SiFiveUARTState *s, const uint8_t *buf,
+ int size)
+{
+ uint64_t current_time = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+
+ if (size > fifo8_num_free(&s->tx_fifo)) {
+ size = fifo8_num_free(&s->tx_fifo);
+ qemu_log_mask(LOG_GUEST_ERROR, "sifive_uart: TX FIFO overflow");
+ }
+
+ fifo8_push_all(&s->tx_fifo, buf, size);
+
+ if (fifo8_is_full(&s->tx_fifo)) {
+ s->txfifo |= SIFIVE_UART_TXFIFO_FULL;
+ }
+
+ timer_mod(s->fifo_trigger_handle, current_time + 100);
Preferably using a #define instead of this magic '100' value (no
need to repost):
Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>
+}
