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

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,
Daniel


> 
> Regards
> Anirudh Srinivasan