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hw/char: sifive_uart: Print uart characters async

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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.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240910045419.1252277-3-alistair.francis@wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
This commit is contained in:
Alistair Francis 2024-08-15 10:57:28 +10:00
parent 4a0e8ca322
commit 53c1557b23
2 changed files with 105 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

16
include/hw/char/sifive_uart.h
View file

@ -24,6 +24,7 @@
#include "hw/qdev-properties.h"
#include "hw/sysbus.h"
#include "qom/object.h"
#include "qemu/fifo8.h"
enum {
SIFIVE_UART_TXFIFO = 0,
@ -48,9 +49,13 @@ enum {
SIFIVE_UART_IP_RXWM = 2 /* Receive watermark interrupt pending */
};
#define SIFIVE_UART_TXFIFO_FULL 0x80000000
#define SIFIVE_UART_GET_TXCNT(txctrl) ((txctrl >> 16) & 0x7)
#define SIFIVE_UART_GET_RXCNT(rxctrl) ((rxctrl >> 16) & 0x7)
#define SIFIVE_UART_RX_FIFO_SIZE 8
#define SIFIVE_UART_TX_FIFO_SIZE 8
#define TYPE_SIFIVE_UART "riscv.sifive.uart"
OBJECT_DECLARE_SIMPLE_TYPE(SiFiveUARTState, SIFIVE_UART)
@ -63,13 +68,20 @@ struct SiFiveUARTState {
qemu_irq irq;
MemoryRegion mmio;
CharBackend chr;
uint8_t rx_fifo[SIFIVE_UART_RX_FIFO_SIZE];
uint8_t rx_fifo_len;
uint32_t txfifo;
uint32_t ie;
uint32_t ip;
uint32_t txctrl;
uint32_t rxctrl;
uint32_t div;
uint8_t rx_fifo[SIFIVE_UART_RX_FIFO_SIZE];
uint8_t rx_fifo_len;
Fifo8 tx_fifo;
QEMUTimer *fifo_trigger_handle;
};
SiFiveUARTState *sifive_uart_create(MemoryRegion *address_space, hwaddr base,