On Wed, Jun 17, 2026 at 5:03 AM Kuan-Wei Chiu <[email protected]> wrote:
>
> Add the dw8250 uart support. This hardware is a widely used 16550A
> derivative that includes additional registers.
>
> Without this specific device support, the Linux 8250_dw driver fails to
> probe the extended registers (UCV, CPR, etc.), which are essential for
> correct feature detection:
>
> [ 0.293566] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
> [ 0.306929] Oops - store (or AMO) access fault [#1]
> [ 0.307020] Modules linked in:
> [ 0.307192] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.0.0 #1
> PREEMPTLAZY
> [ 0.307250] Hardware name: Milk-V Duo (DT)
> [ 0.307294] epc : dw8250_setup_port+0x22/0x520
> [ 0.307504] ra : dw8250_probe+0x57e/0x5b8
> [ 0.307518] epc : ffffffff80708dd6 ra : ffffffff8070a49e sp :
> ffffffc60000b820
> [ 0.307525] gp : ffffffff81a32ba8 tp : ffffffd602180cc0 t0 :
> 0000000000000073
> [ 0.307533] t1 : 000000000000006c t2 : 0000000000000000 s0 :
> ffffffc60000b830
> [ 0.307539] s1 : ffffffd6028c8640 a0 : ffffffc60000b848 a1 :
> ffffffff813162c1
> [ 0.307546] a2 : ffffffff813162c0 a3 : ffffffd6028c8640 a4 :
> ffffffc60002d0b4
> [ 0.307552] a5 : 0000000000000001 a6 : 0000000000000094 a7 :
> 0000000000000060
> [ 0.307558] s2 : ffffffd60225d410 s3 : ffffffd60225d400 s4 :
> 0000000000000000
> [ 0.307573] s5 : ffffffff80e31a48 s6 : 0000000000000008 s7 :
> 0000000000000000
> [ 0.307584] s8 : 0000000000000149 s9 : 0000000000000000 s10:
> 0000000000000000
> [ 0.307590] s11: 0000000000000000 t3 : ffffffd602007c00 t4 :
> ffffffff81601540
> [ 0.307604] t5 : 0000000000000003 t6 : ffffffd602a42f82 ssp :
> 0000000000000000
> [ 0.307611] status: 0000000200000120 badaddr: ffffffc60002d0b4 cause:
> 0000000000000007
> [ 0.307652] [<ffffffff80708dd6>] dw8250_setup_port+0x22/0x520
> [ 0.307695] [<ffffffff8070a49e>] dw8250_probe+0x57e/0x5b8
> [ 0.307702] [<ffffffff80731f0e>] platform_probe+0x46/0x80
> [ 0.307708] [<ffffffff8072f67c>] really_probe+0x84/0x22c
> [ 0.307715] [<ffffffff8072f880>] __driver_probe_device+0x5c/0xd4
> [ 0.307721] [<ffffffff8072f9be>] driver_probe_device+0x2e/0xf4
> [ 0.307727] [<ffffffff8072fbe6>] __driver_attach+0x6e/0x14c
> [ 0.307734] [<ffffffff8072d5f0>] bus_for_each_dev+0x60/0xb0
> [ 0.307740] [<ffffffff8072f1b2>] driver_attach+0x1a/0x24
> [ 0.307746] [<ffffffff8072e8da>] bus_add_driver+0xca/0x1d8
> [ 0.307752] [<ffffffff80730aaa>] driver_register+0x3e/0xdc
> [ 0.307757] [<ffffffff80731c54>] __platform_driver_register+0x1c/0x24
> [ 0.307779] [<ffffffff80c334f6>] dw8250_platform_driver_init+0x1a/0x24
> [ 0.307793] [<ffffffff80011992>] do_one_initcall+0x4e/0x2a4
> [ 0.307800] [<ffffffff80c01362>] kernel_init_freeable+0x226/0x2b0
> [ 0.307807] [<ffffffff80bc3798>] kernel_init+0x1c/0x144
> [ 0.307813] [<ffffffff8001361c>] ret_from_fork_kernel+0x18/0x164
> [ 0.307820] [<ffffffff80bcefb6>] ret_from_fork_kernel_asm+0x16/0x18
> [ 0.307914] Code: 3683 2085 0b63 32f7 000f 0140 6918 4785 0713 0b47 (c31c)
> 2583
> [ 0.308041] ---[ end trace 0000000000000000 ]---
> [ 0.308180] Kernel panic - not syncing: Fatal exception in interrupt
> [ 0.315760] ---[ end Kernel panic - not syncing: Fatal exception in
> interrupt ]---
>
> Signed-off-by: Kuan-Wei Chiu <[email protected]>
> Reviewed-by: Chao Liu <[email protected]>
> ---
> hw/char/Kconfig | 4 ++
> hw/char/dw8250.c | 118 +++++++++++++++++++++++++++++++++++++++
> hw/char/meson.build | 1 +
> include/hw/char/dw8250.h | 27 +++++++++
> 4 files changed, 150 insertions(+)
> create mode 100644 hw/char/dw8250.c
> create mode 100644 include/hw/char/dw8250.h
>
> diff --git a/hw/char/Kconfig b/hw/char/Kconfig
> index 020c0a84bb..418d99b757 100644
> --- a/hw/char/Kconfig
> +++ b/hw/char/Kconfig
> @@ -95,3 +95,7 @@ config IP_OCTAL_232
> bool
> default y
> depends on IPACK
> +
> +config DW8250
> + bool
> + select SERIAL
> diff --git a/hw/char/dw8250.c b/hw/char/dw8250.c
> new file mode 100644
> index 0000000000..4ec829ceaf
> --- /dev/null
> +++ b/hw/char/dw8250.c
> @@ -0,0 +1,118 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Synopsys DesignWare APB UART (DW 8250)
> + *
> + * Copyright (c) 2026 Kuan-Wei Chiu <[email protected]>
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "hw/char/dw8250.h"
> +#include "hw/core/qdev-properties.h"
> +#include "hw/core/qdev-properties-system.h"
> +
> +#define DW_UART_REGION_SIZE 0x100
> +
> +#define DW_UART_RE_EN 0xB4 /* Receiver Output Enable Register */
> +#define DW_UART_DLF 0xC0 /* Divisor Latch Fraction Register */
> +#define DW_UART_CPR 0xF4 /* Component Parameter Register */
> +#define DW_UART_UCV 0xF8 /* UART Component Version */
> +#define DW_UART_CTR 0xFC /* Component Type Register */
> +
> +#define DW_UART_UCV_VALUE 0x3332332A /* "323*" -> v3.23a */
> +#define DW_UART_CTR_VALUE 0x44570110 /* "DW" */
> +
> +static uint64_t dw8250_ext_read(void *opaque, hwaddr addr, unsigned int size)
> +{
> + switch (addr) {
> + case DW_UART_UCV:
> + return DW_UART_UCV_VALUE;
> + case DW_UART_CPR:
> + return 0x00000000; /* No advanced features (DMA, extra FIFOs) */
> + case DW_UART_CTR:
> + return DW_UART_CTR_VALUE;
> +
> + case DW_UART_RE_EN:
> + case DW_UART_DLF:
> + /*
> + * Return 0 to indicate these optional features
> + * (RS485 and Fractional Divisor) are not implemented.
> + */
> + return 0x00000000;
> +
> + default:
> + return 0;
> + }
> +}
> +
> +static void dw8250_ext_write(void *opaque, hwaddr addr, uint64_t val,
> unsigned int size)
> +{
> +}
> +
> +static const MemoryRegionOps dw8250_ext_ops = {
> + .read = dw8250_ext_read,
> + .write = dw8250_ext_write,
> + .endianness = DEVICE_LITTLE_ENDIAN,
> + .valid.min_access_size = 4,
> + .valid.max_access_size = 4,
> +};
This should be 1 not 4. The DesignWare DW_apb_uart Databook says "All
APB slave programming registers are aligned on 32-bit boundaries,
irrespective of the APB bus size." So even though the registers are
32-bit aligned an 8 or 16-bit APB bus width is valid. You can use impl
to prevent the read/write function from having to handle variable size
accesses.
- .valid.min_access_size = 4,
+ .impl.min_access_size = 4,
+ .impl.max_access_size = 4,
+ .valid.min_access_size = 1,
-
Portia
> +
> +static void dw8250_instance_init(Object *obj)
> +{
> + DW8250State *s = DW8250(obj);
> +
> + s->serial_mm = qdev_new("serial-mm");
> + object_property_add_child(obj, "serial-mm", OBJECT(s->serial_mm));
> + object_property_add_alias(obj, "chardev", OBJECT(s->serial_mm),
> "chardev");
> +}
> +
> +static void dw8250_realize(DeviceState *dev, Error **errp)
> +{
> + DW8250State *s = DW8250(dev);
> + SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> + SysBusDevice *serial_sbd = SYS_BUS_DEVICE(s->serial_mm);
> +
> + memory_region_init(&s->container, OBJECT(dev), "dw8250-container",
> + DW_UART_REGION_SIZE);
> + sysbus_init_mmio(sbd, &s->container);
> +
> + qdev_prop_set_uint8(s->serial_mm, "regshift", s->regshift);
> + qdev_prop_set_uint8(s->serial_mm, "endianness", DEVICE_LITTLE_ENDIAN);
> + sysbus_realize(serial_sbd, errp);
> +
> + memory_region_init_io(&s->ext_iomem, OBJECT(dev), &dw8250_ext_ops, s,
> + "dw8250-ext", DW_UART_REGION_SIZE);
> + memory_region_add_subregion(&s->container, 0, &s->ext_iomem);
> +
> + memory_region_add_subregion_overlap(&s->container, 0,
> + sysbus_mmio_get_region(serial_sbd,
> 0), 1);
> +
> + sysbus_pass_irq(sbd, serial_sbd);
> +}
> +
> +static const Property dw8250_properties[] = {
> + DEFINE_PROP_UINT8("regshift", DW8250State, regshift, 2),
> +};
> +
> +static void dw8250_class_init(ObjectClass *klass, const void *data)
> +{
> + DeviceClass *dc = DEVICE_CLASS(klass);
> +
> + dc->realize = dw8250_realize;
> + device_class_set_props(dc, dw8250_properties);
> +}
> +
> +static const TypeInfo dw8250_info = {
> + .name = TYPE_DW8250,
> + .parent = TYPE_SYS_BUS_DEVICE,
> + .instance_size = sizeof(DW8250State),
> + .instance_init = dw8250_instance_init,
> + .class_init = dw8250_class_init,
> +};
> +
> +static void dw8250_register_types(void)
> +{
> + type_register_static(&dw8250_info);
> +}
> +
> +type_init(dw8250_register_types)
> diff --git a/hw/char/meson.build b/hw/char/meson.build
> index fc3d7ee506..b2250ee6ae 100644
> --- a/hw/char/meson.build
> +++ b/hw/char/meson.build
> @@ -38,6 +38,7 @@ system_ss.add(when: 'CONFIG_STM32L4X5_USART', if_true:
> files('stm32l4x5_usart.c'
> system_ss.add(when: 'CONFIG_MCHP_PFSOC_MMUART', if_true:
> files('mchp_pfsoc_mmuart.c'))
> system_ss.add(when: 'CONFIG_HTIF', if_true: files('riscv_htif.c'))
> system_ss.add(when: 'CONFIG_GOLDFISH_TTY', if_true: files('goldfish_tty.c'))
> +system_ss.add(when: 'CONFIG_DW8250', if_true: files('dw8250.c'))
>
> specific_ss.add(when: 'CONFIG_TERMINAL3270', if_true:
> files('terminal3270.c'))
> specific_ss.add(when: 'CONFIG_PSERIES', if_true: files('spapr_vty.c'))
> diff --git a/include/hw/char/dw8250.h b/include/hw/char/dw8250.h
> new file mode 100644
> index 0000000000..59396ad202
> --- /dev/null
> +++ b/include/hw/char/dw8250.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Synopsys DesignWare APB UART (DW 8250)
> + *
> + * Copyright (c) 2026 Kuan-Wei Chiu <[email protected]>
> + */
> +
> +#ifndef HW_CHAR_DW8250_H
> +#define HW_CHAR_DW8250_H
> +
> +#include "hw/core/sysbus.h"
> +#include "qom/object.h"
> +
> +#define TYPE_DW8250 "dw8250"
> +OBJECT_DECLARE_SIMPLE_TYPE(DW8250State, DW8250)
> +
> +struct DW8250State {
> + SysBusDevice parent_obj;
> +
> + MemoryRegion container;
> + MemoryRegion ext_iomem;
> + DeviceState *serial_mm;
> +
> + uint8_t regshift;
> +};
> +
> +#endif
> --
> 2.54.0.1136.gdb2ca164c4-goog
>
>
