Re: [PATCH v5 07/15] emul/ns16x50: implement FCR register (write-only)

[dmukhin@xen.org]

On Fri, Aug 29, 2025 at 01:38:02PM -0700, Stefano Stabellini wrote:
> On Thu, 28 Aug 2025, dmukhin@xen.org wrote:
> > From: Denis Mukhin <dmukhin@ford.com> 
> > 
> > Add emulation logic for FCR register.
> > 
> > Note, that does not hooks FIFO interrupt moderation to the FIFO management
> > code.
> > 
> > Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> > ---
> > Changes since v4:
> > - new patch
> > ---
> >  xen/common/emul/vuart/ns16x50.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > diff --git a/xen/common/emul/vuart/ns16x50.c b/xen/common/emul/vuart/ns16x50.c
> > index efb2f4c6441c..65ca96dd8bd3 100644
> > --- a/xen/common/emul/vuart/ns16x50.c
> > +++ b/xen/common/emul/vuart/ns16x50.c
> > @@ -363,6 +363,30 @@ static int ns16x50_io_write8(
> >  
> >              break;
> >  
> > +        case UART_FCR: /* WO */
> > +            if ( val & UART_FCR_RESERVED0 )
> > +                ns16x50_warn(vdev, "FCR: attempt to set reserved bit: %x\n",
> > +                             UART_FCR_RESERVED0);
> > +
> > +            if ( val & UART_FCR_RESERVED1 )
> > +                ns16x50_warn(vdev, "FCR: attempt to set reserved bit: %x\n",
> > +                             UART_FCR_RESERVED1);
> > +
> > +            if ( val & UART_FCR_CLRX )
> > +                ns16x50_fifo_rx_reset(vdev);
> > +
> > +            if ( val & UART_FCR_CLTX )
> > +                ns16x50_fifo_tx_flush(vdev);
> 
> Should UART_FCR_CLTX actually emit data or only clear the buffer?

Yes, thanks; should be just "tx_reset".

> 
> set UART_IIR_THR ?

Will do, thanks.

> 
> 
> > +
> > +            if ( val & UART_FCR_ENABLE )
> > +                val &= UART_FCR_ENABLE | UART_FCR_DMA | UART_FCR_TRG_MASK;
> > +            else
> > +                val = 0;
> > +
> > +            regs[UART_FCR] = val;
> 
> 
> ns16x50_irq_check ?

ns16x50_irq_check() is poked after the switch statement.

> 
> 
> > +            break;
> > +
> >          default:
> >              rc = -EINVAL;
> >              break;
> > -- 
> > 2.51.0
> >