On Fri, 5 Sep 2025, dmukhin@xen.org wrote:
> From: Denis Mukhin <dmukhin@ford.com>
>
> Add LCR/LSR registers implementation to the I/O port handler.
>
> Add implementation of ns16x50_dlab_get() and ns16x50_iir_check_lsi().
>
> Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> ---
> Changes since v5:
> - Moved earlier in the series so follow on patches (THR/RBR) could make use of
> LSR bits more naturally
> - Link to v5: https://lore.kernel.org/xen-devel/20250828235409.2835815-9-dmukhin@ford.com/
> ---
> xen/common/emul/vuart/ns16x50.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/xen/common/emul/vuart/ns16x50.c b/xen/common/emul/vuart/ns16x50.c
> index a7429c84c36e..9d1fe0284362 100644
> --- a/xen/common/emul/vuart/ns16x50.c
> +++ b/xen/common/emul/vuart/ns16x50.c
> @@ -88,12 +88,12 @@ struct vuart_ns16x50 {
>
> static uint8_t ns16x50_dlab_get(const struct vuart_ns16x50 *vdev)
> {
> - return 0;
> + return vdev->regs[UART_LCR] & UART_LCR_DLAB ? 1 : 0;
> }
>
> static bool cf_check ns16x50_iir_check_lsi(const struct vuart_ns16x50 *vdev)
> {
> - return false;
> + return vdev->regs[UART_LSR] & UART_LSR_MASK;
> }
>
> static bool cf_check ns16x50_iir_check_rda(const struct vuart_ns16x50 *vdev)
> @@ -226,11 +226,16 @@ static int ns16x50_io_write8(
> regs[UART_IER] = val & UART_IER_MASK;
> break;
>
> + case UART_LCR:
> + regs[UART_LCR] = val;
> + break;
> +
> /* NB: Firmware (e.g. OVMF) may rely on SCR presence. */
> case UART_SCR:
> regs[UART_SCR] = val;
> break;
>
> + case UART_LSR: /* RO */
> default:
> rc = -EINVAL;
> break;
> @@ -312,6 +317,15 @@ static int ns16x50_io_read8(
> val = ns16x50_iir_get(vdev);
> break;
>
> + case UART_LCR:
> + val = regs[UART_LCR];
> + break;
> +
> + case UART_LSR:
> + val = regs[UART_LSR] | UART_LSR_THRE | UART_LSR_TEMT;
> + regs[UART_LSR] = val & ~UART_LSR_MASK;
> + break;
> +
> case UART_SCR:
> val = regs[UART_SCR];
> break;
> --
> 2.51.0
>