Re: [PATCH] hw/char: disable ibex uart receive if the buffer is full

[Alistair Francis <alistair23@gmail.com>]

On Mon, Feb 15, 2021 at 9:06 PM Alexander Wagner
<alexander.wagner@ulal.de> wrote:
>
> Not disabling the UART leads to QEMU overwriting the UART receive buffer with
> the newest received byte. The rx_level variable is added to allow the use of
> the existing OpenTitan driver libraries.
>
> Signed-off-by: Alexander Wagner <alexander.wagner@ulal.de>

Thanks for the patch!

I'm glad to see others using OT on QEMU.

> ---
>  hw/char/ibex_uart.c         | 20 +++++++++++++++-----
>  include/hw/char/ibex_uart.h |  4 ++++
>  2 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/hw/char/ibex_uart.c b/hw/char/ibex_uart.c
> index 89f1182c9b..dac09d53d6 100644
> --- a/hw/char/ibex_uart.c
> +++ b/hw/char/ibex_uart.c
> @@ -66,7 +66,8 @@ static int ibex_uart_can_receive(void *opaque)
>  {
>      IbexUartState *s = opaque;
>
> -    if (s->uart_ctrl & R_CTRL_RX_ENABLE_MASK) {
> +    if ((s->uart_ctrl & R_CTRL_RX_ENABLE_MASK)
> +           && !(s->uart_status & R_STATUS_RXFULL_MASK)) {
>          return 1;
>      }
>
> @@ -83,6 +84,8 @@ static void ibex_uart_receive(void *opaque, const uint8_t *buf, int size)
>
>      s->uart_status &= ~R_STATUS_RXIDLE_MASK;
>      s->uart_status &= ~R_STATUS_RXEMPTY_MASK;
> +    s->uart_status |= R_STATUS_RXFULL_MASK;

Doesn't this mean we set RXFULL on every receive? Shouldn't this check
the rx_level first?

Alistair

> +    s->rx_level += 1;
>
>      if (size > rx_fifo_level) {
>          s->uart_intr_state |= R_INTR_STATE_RX_WATERMARK_MASK;
> @@ -199,6 +202,7 @@ static void ibex_uart_reset(DeviceState *dev)
>      s->uart_timeout_ctrl = 0x00000000;
>
>      s->tx_level = 0;
> +    s->rx_level = 0;
>
>      s->char_tx_time = (NANOSECONDS_PER_SECOND / 230400) * 10;
>
> @@ -243,11 +247,15 @@ static uint64_t ibex_uart_read(void *opaque, hwaddr addr,
>
>      case R_RDATA:
>          retvalue = s->uart_rdata;
> -        if (s->uart_ctrl & R_CTRL_RX_ENABLE_MASK) {
> +        if ((s->uart_ctrl & R_CTRL_RX_ENABLE_MASK) && (s->rx_level > 0)) {
>              qemu_chr_fe_accept_input(&s->chr);
>
> -            s->uart_status |= R_STATUS_RXIDLE_MASK;
> -            s->uart_status |= R_STATUS_RXEMPTY_MASK;
> +            s->rx_level -= 1;
> +            s->uart_status &= ~R_STATUS_RXFULL_MASK;
> +            if (s->rx_level == 0) {
> +                s->uart_status |= R_STATUS_RXIDLE_MASK;
> +                s->uart_status |= R_STATUS_RXEMPTY_MASK;
> +            }
>          }
>          break;
>      case R_WDATA:
> @@ -261,7 +269,8 @@ static uint64_t ibex_uart_read(void *opaque, hwaddr addr,
>      case R_FIFO_STATUS:
>          retvalue = s->uart_fifo_status;
>
> -        retvalue |= s->tx_level & 0x1F;
> +        retvalue |= (s->rx_level & 0x1F) << R_FIFO_STATUS_RXLVL_SHIFT;
> +        retvalue |= (s->tx_level & 0x1F) << R_FIFO_STATUS_TXLVL_SHIFT;
>
>          qemu_log_mask(LOG_UNIMP,
>                        "%s: RX fifos are not supported\n", __func__);
> @@ -364,6 +373,7 @@ static void ibex_uart_write(void *opaque, hwaddr addr,
>          s->uart_fifo_ctrl = value;
>
>          if (value & R_FIFO_CTRL_RXRST_MASK) {
> +            s->rx_level = 0;
>              qemu_log_mask(LOG_UNIMP,
>                            "%s: RX fifos are not supported\n", __func__);
>          }
> diff --git a/include/hw/char/ibex_uart.h b/include/hw/char/ibex_uart.h
> index 03d19e3f6f..546f958eb8 100644
> --- a/include/hw/char/ibex_uart.h
> +++ b/include/hw/char/ibex_uart.h
> @@ -62,6 +62,8 @@ REG32(FIFO_CTRL, 0x1c)
>      FIELD(FIFO_CTRL, RXILVL, 2, 3)
>      FIELD(FIFO_CTRL, TXILVL, 5, 2)
>  REG32(FIFO_STATUS, 0x20)
> +    FIELD(FIFO_STATUS, TXLVL, 0, 5)
> +    FIELD(FIFO_STATUS, RXLVL, 16, 5)
>  REG32(OVRD, 0x24)
>  REG32(VAL, 0x28)
>  REG32(TIMEOUT_CTRL, 0x2c)
> @@ -82,6 +84,8 @@ struct IbexUartState {
>      uint8_t tx_fifo[IBEX_UART_TX_FIFO_SIZE];
>      uint32_t tx_level;
>
> +    uint32_t rx_level;
> +
>      QEMUTimer *fifo_trigger_handle;
>      uint64_t char_tx_time;
>
> --
> 2.25.1
>
>