On Thu, Aug 15, 2024 at 6:27 PM Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk> wrote: > > On 15/08/2024 02:54, Alistair Francis wrote: > > > The current approach of using qemu_chr_fe_write() and ignoring the > > return values results in dropped charecters [1]. > > > > Let's update the SiFive UART to use a async sifive_uart_xmit() function > > to transmit the charecters and apply back preassure to the guest with > > the SIFIVE_UART_TXFIFO_FULL status. > > > > This should avoid dropped charecters and more realisiticly model the > > hardware. > > > > 1: https://gitlab.com/qemu-project/qemu/-/issues/2114 > > > > Signed-off-by: Alistair Francis <alistair.fran...@wdc.com> > > --- > > include/hw/char/sifive_uart.h | 17 +++++++- > > hw/char/sifive_uart.c | 81 +++++++++++++++++++++++++++++++++-- > > 2 files changed, 92 insertions(+), 6 deletions(-) > > > > diff --git a/include/hw/char/sifive_uart.h b/include/hw/char/sifive_uart.h > > index 7f6c79f8bd..73379457a0 100644 > > --- a/include/hw/char/sifive_uart.h > > +++ b/include/hw/char/sifive_uart.h > > @@ -48,9 +48,13 @@ 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 +67,22 @@ 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; > > + > > + uint8_t tx_fifo[SIFIVE_UART_TX_FIFO_SIZE]; > > + uint32_t tx_level; > > + > > + QEMUTimer *fifo_trigger_handle; > > + uint64_t char_tx_time; > > }; > > > > SiFiveUARTState *sifive_uart_create(MemoryRegion *address_space, hwaddr > > base, > > diff --git a/hw/char/sifive_uart.c b/hw/char/sifive_uart.c > > index 7fc6787f69..f517500df4 100644 > > --- a/hw/char/sifive_uart.c > > +++ b/hw/char/sifive_uart.c > > @@ -64,6 +64,64 @@ static void sifive_uart_update_irq(SiFiveUARTState *s) > > } > > } > > > > +static gboolean sifive_uart_xmit(void *do_not_use, GIOCondition cond, > > + void *opaque) > > +{ > > + SiFiveUARTState *s = opaque; > > + int ret; > > + > > + /* instant drain the fifo when there's no back-end */ > > + if (!qemu_chr_fe_backend_connected(&s->chr)) { > > + s->tx_level = 0; > > + return G_SOURCE_REMOVE; > > + } > > + > > + ret = qemu_chr_fe_write(&s->chr, s->tx_fifo, s->tx_level); > > + > > + if (ret >= 0) { > > + s->tx_level -= ret; > > + memmove(s->tx_fifo, s->tx_fifo + ret, s->tx_level); > > + } > > + > > + if (s->tx_level) { > > + guint r = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP, > > + sifive_uart_xmit, s); > > + if (!r) { > > + s->tx_level = 0; > > + return G_SOURCE_REMOVE; > > + } > > + } > > + > > + /* Clear the TX Full bit */ > > + if (s->tx_level != SIFIVE_UART_TX_FIFO_SIZE) { > > + s->txfifo &= ~SIFIVE_UART_TXFIFO_FULL; > > + } > > + > > + sifive_uart_update_irq(s); > > + return G_SOURCE_REMOVE; > > +} > > + > > +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 > SIFIVE_UART_TX_FIFO_SIZE - s->tx_level) { > > + size = SIFIVE_UART_TX_FIFO_SIZE - s->tx_level; > > + qemu_log_mask(LOG_GUEST_ERROR, "sifive_uart: TX FIFO overflow"); > > + } > > + > > + memcpy(s->tx_fifo + s->tx_level, buf, 1); > > + s->tx_level += 1; > > + > > + if (s->tx_level == SIFIVE_UART_TX_FIFO_SIZE) { > > + s->txfifo |= SIFIVE_UART_TXFIFO_FULL; > > + } > > + > > + timer_mod(s->fifo_trigger_handle, current_time + > > + (s->char_tx_time * 4)); > > +} > > + > > static uint64_t > > sifive_uart_read(void *opaque, hwaddr addr, unsigned int size) > > { > > @@ -82,7 +140,7 @@ sifive_uart_read(void *opaque, hwaddr addr, unsigned int > > size) > > return 0x80000000; > > > > case SIFIVE_UART_TXFIFO: > > - return 0; /* Should check tx fifo */ > > + return s->txfifo; > > case SIFIVE_UART_IE: > > return s->ie; > > case SIFIVE_UART_IP: > > @@ -106,12 +164,10 @@ sifive_uart_write(void *opaque, hwaddr addr, > > { > > SiFiveUARTState *s = opaque; > > uint32_t value = val64; > > - unsigned char ch = value; > > > > switch (addr) { > > case SIFIVE_UART_TXFIFO: > > - qemu_chr_fe_write(&s->chr, &ch, 1); > > - sifive_uart_update_irq(s); > > + sifive_uart_write_tx_fifo(s, (uint8_t *) &value, 1); > > return; > > case SIFIVE_UART_IE: > > s->ie = val64; > > @@ -131,6 +187,13 @@ sifive_uart_write(void *opaque, hwaddr addr, > > __func__, (int)addr, (int)value); > > } > > > > +static void fifo_trigger_update(void *opaque) > > +{ > > + SiFiveUARTState *s = opaque; > > + > > + sifive_uart_xmit(NULL, G_IO_OUT, s); > > +} > > + > > static const MemoryRegionOps sifive_uart_ops = { > > .read = sifive_uart_read, > > .write = sifive_uart_write, > > @@ -197,6 +260,9 @@ static void sifive_uart_realize(DeviceState *dev, Error > > **errp) > > { > > SiFiveUARTState *s = SIFIVE_UART(dev); > > > > + s->fifo_trigger_handle = timer_new_ns(QEMU_CLOCK_VIRTUAL, > > + fifo_trigger_update, s); > > + > > qemu_chr_fe_set_handlers(&s->chr, sifive_uart_can_rx, sifive_uart_rx, > > sifive_uart_event, sifive_uart_be_change, s, > > NULL, true); > > @@ -206,12 +272,19 @@ static void sifive_uart_realize(DeviceState *dev, > > Error **errp) > > static void sifive_uart_reset_enter(Object *obj, ResetType type) > > { > > SiFiveUARTState *s = SIFIVE_UART(obj); > > + > > + s->txfifo = 0; > > s->ie = 0; > > s->ip = 0; > > s->txctrl = 0; > > s->rxctrl = 0; > > s->div = 0; > > + > > + s->tx_level = 0; > > s->rx_fifo_len = 0; > > + > > + memset(s->rx_fifo, 0, SIFIVE_UART_RX_FIFO_SIZE); > > + memset(s->tx_fifo, 0, SIFIVE_UART_TX_FIFO_SIZE); > > } > > > > static void sifive_uart_reset_hold(Object *obj, ResetType type) > > Have you considered using a Fifo8 here? This avoids having to manually roll > your own > FIFO implementation.
Yeah, I will convert it to a Fifo8. Alistair > > > ATB, > > Mark. >
