Re: [PATCH 08/13] hw/riscv/fdt-common, virt.c, tt_atlantis.c: add create_fdt_uart()

On Wed, Aug 26, 2026 at 10:05 AM Daniel Henrique Barboza
<[email protected]> wrote:
>
>
>
> On 8/26/2026 11:53 AM, Anirudh Srinivasan wrote:
> > Hi Daniel,
> >
> > On Tue, Aug 25, 2026 at 4:24 PM Daniel Henrique Barboza
> > <[email protected]> wrote:
> >>
> >> Add a common uart FDT helper to be used by 'virt' and 'tt-atlantis'.
> >>
> >> To accomodate both boards the helper is doing the following:
> >> - an 'additional_reg_props' flag is used to control whether we want
> >>    'reg-shift' and 'reg-io-width' elements added.  OpenSBI won't boot
> >>    with the tt-atlantis board without them, but 'virt' can't deal with
> >>    them being added unconditionally either.
> >> - an 'is_serial0' flag is added to control whether we need to set
> >>    additional properties related to the first serial.  This is required
> >>    because the 'virt' board adds two uarts in the FDT.
> >>
> >> No FDT changes intended.
> >>
> >> Signed-off-by: Daniel Henrique Barboza <[email protected]>
> >> ---
> >>   hw/riscv/fdt-common.c         | 39 +++++++++++++++++++++++++++++++
> >>   hw/riscv/tt_atlantis.c        | 21 +----------------
> >>   hw/riscv/virt.c               | 44 +++++++----------------------------
> >>   include/hw/riscv/fdt-common.h |  4 ++++
> >>   4 files changed, 52 insertions(+), 56 deletions(-)
> >>
> >> diff --git a/hw/riscv/fdt-common.c b/hw/riscv/fdt-common.c
> >> index f31cc9d3cc..b3f3af3762 100644
> >> --- a/hw/riscv/fdt-common.c
> >> +++ b/hw/riscv/fdt-common.c
> >> @@ -791,3 +791,42 @@ void create_fdt_socket_aclint(void *fdt, ACLINTFdtProps *props,
> >>           g_free(name);
> >>       }
> >>   }
> >> +
> >> +void create_fdt_uart(void *fdt, const MemMapEntry *uart_mem,
> >> +                     int uart_irq, int aia_type,
> >> +                     bool additional_reg_props, bool is_serial0,
> >> +                     uint32_t irq_mmio_phandle)
> >> +{
> >> +    g_autofree char *name = NULL;
> >> +
> >> +    name = g_strdup_printf("/soc/serial@%"HWADDR_PRIx, uart_mem->base);
> >> +    qemu_fdt_add_subnode(fdt, name);
> >> +    qemu_fdt_setprop_string(fdt, name, "compatible", "ns16550a");
> >> +    qemu_fdt_setprop_sized_cells(fdt, name, "reg",
> >> +                                 2, uart_mem->base,
> >> +                                 2, uart_mem->size);
> >> +
> >> +    /*
> >> +     * The tt-atlantis board requires these extra props in the
> >> +     * DT, but adding them unconditionally will break OpenSBI
> >> +     * for 'virt'.
> >> +     */
> >> +    if (additional_reg_props) {
> >> +        qemu_fdt_setprop_cell(fdt, name, "reg-shift", 2);
> >> +        qemu_fdt_setprop_cell(fdt, name, "reg-io-width", 4);
> >> +    }
> >
> > I think the issue is that atlantis uses a uart that has 32 bit
> > register spacing (0x0, 0x4, 0x8, 0xc....) rather than 8 bit spacing
> > (0x0, 0x1, 0x2...). So rather than "additional_reg_props", would a
> > name like "word_addressing" or "32_bit_spacing" make sense?
>
> Works for me.  I'll rename it in v2.

Thanks.

Reviewed-by: Anirudh Srinivasan <[email protected]>

>
> Thanks,
> Daniel
>
>
> >
> > Regards
> > Anirudh Srinivasan
>