[PATCH v2 3/6] hw/misc: Add Sophgo CV1800B clock controller

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Add a stub for the CV1800B clock controller. This is specifically
required for the SDHCI controller to function correctly under Linux.

The Linux 'sophgo,cv1800-clk' driver probes this device to determine
the clock tree configuration. This implementation sets the bypass
registers (CLK_BYP_0 and CLK_BYP_1) to 0xFFFFFFFF during reset,
matching the POR default state. This bypasses the PLLs and allows the
SDHCI and other peripherals to operate using the 25MHz reference clock.

Without this device, the SD card driver fails to initialize, preventing
the system from mounting the root filesystem from the SD card:

[    0.888739] Waiting for root device /dev/mmcblk0...
[   10.727739] mmc0: Timeout waiting for hardware cmd interrupt.
[   10.728042] mmc0: sdhci: ============ SDHCI REGISTER DUMP ===========
[   10.728356] mmc0: sdhci: Sys addr:  0x00000002 | Version:  0x00002402
[   10.728618] mmc0: sdhci: Blk size:  0x00000000 | Blk cnt:  0x00000000
[   10.728919] mmc0: sdhci: Argument:  0x00000000 | Trn mode: 0x00000000
[   10.729271] mmc0: sdhci: Present:   0x01ff0000 | Host ctl: 0x00000001
[   10.729591] mmc0: sdhci: Power:     0x0000000f | Blk gap:  0x00000000
[   10.729903] mmc0: sdhci: Wake-up:   0x00000000 | Clock:    0x00000000
[   10.730223] mmc0: sdhci: Timeout:   0x00000000 | Int stat: 0x00000000
[   10.730537] mmc0: sdhci: Int enab:  0x00ff0083 | Sig enab: 0x00ff0083
[   10.730795] mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00000000
[   10.731005] mmc0: sdhci: Caps:      0x056900b9 | Caps_1:   0x00000000
[   10.731211] mmc0: sdhci: Cmd:       0x00000000 | Max curr: 0x00000000
[   10.731415] mmc0: sdhci: Resp[0]:   0x00000000 | Resp[1]:  0x00000000
[   10.731636] mmc0: sdhci: Resp[2]:   0x00000000 | Resp[3]:  0x00000000
[   10.731851] mmc0: sdhci: Host ctl2: 0x00000000
[   10.732018] mmc0: sdhci: ADMA Err:  0x00000000 | ADMA Ptr: 0x00000000
[   10.732229] mmc0: sdhci: ============================================

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 hw/misc/Kconfig               |  3 ++
 hw/misc/cv1800b_clk.c         | 89 +++++++++++++++++++++++++++++++++++
 hw/misc/meson.build           |  1 +
 include/hw/misc/cv1800b_clk.h | 24 ++++++++++
 4 files changed, 117 insertions(+)
 create mode 100644 hw/misc/cv1800b_clk.c
 create mode 100644 include/hw/misc/cv1800b_clk.h

diff --git a/hw/misc/Kconfig b/hw/misc/Kconfig
index 99bdf09219..42cdf771a4 100644
--- a/hw/misc/Kconfig
+++ b/hw/misc/Kconfig
@@ -254,4 +254,7 @@ config IOSB
 config XLNX_VERSAL_TRNG
     bool
 
+config SOPHGO_CV1800B_CLK
+    bool
+
 source macio/Kconfig
diff --git a/hw/misc/cv1800b_clk.c b/hw/misc/cv1800b_clk.c
new file mode 100644
index 0000000000..738f0910db
--- /dev/null
+++ b/hw/misc/cv1800b_clk.c
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Sophgo CV1800B Clock Controller
+ *
+ * Copyright (c) 2026 Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "hw/misc/cv1800b_clk.h"
+
+#define REG_CLK_BYP_0  (0x030 / 4)
+#define REG_CLK_BYP_1  (0x034 / 4)
+
+static uint64_t cv1800b_clk_read(void *opaque, hwaddr addr, unsigned int size)
+{
+    CV1800BClkState *s = opaque;
+    uint32_t val = 0;
+
+    if ((addr / 4) < ARRAY_SIZE(s->regs)) {
+        val = s->regs[addr / 4];
+    }
+
+    return val;
+}
+
+static void cv1800b_clk_write(void *opaque, hwaddr addr, uint64_t val, unsigned int size)
+{
+    CV1800BClkState *s = opaque;
+
+    if ((addr / 4) < ARRAY_SIZE(s->regs)) {
+        s->regs[addr / 4] = val;
+    }
+}
+
+static const MemoryRegionOps cv1800b_clk_ops = {
+    .read = cv1800b_clk_read,
+    .write = cv1800b_clk_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid = {
+        .min_access_size = 4,
+        .max_access_size = 4,
+    },
+};
+
+static void cv1800b_clk_reset_hold(Object *obj, ResetType type)
+{
+    CV1800BClkState *s = CV1800B_CLK(obj);
+
+    memset(s->regs, 0, sizeof(s->regs));
+
+    /*
+     * TODO: Implement proper PLL state machines.
+     * For now, use POR default to bypass PLLs and boot via 25MHz XTAL.
+     */
+    s->regs[REG_CLK_BYP_0] = 0xFFFFFFFF;
+    s->regs[REG_CLK_BYP_1] = 0xFFFFFFFF;
+}
+
+static void cv1800b_clk_init(Object *obj)
+{
+    CV1800BClkState *s = CV1800B_CLK(obj);
+
+    memory_region_init_io(&s->iomem, obj, &cv1800b_clk_ops, s,
+                            TYPE_CV1800B_CLK, 0x1000);
+    sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->iomem);
+}
+
+static void cv1800b_clk_class_init(ObjectClass *klass, const void *data)
+{
+    ResettableClass *rc = RESETTABLE_CLASS(klass);
+
+    rc->phases.hold = cv1800b_clk_reset_hold;
+}
+
+static const TypeInfo cv1800b_clk_info = {
+    .name = TYPE_CV1800B_CLK,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(CV1800BClkState),
+    .instance_init = cv1800b_clk_init,
+    .class_init = cv1800b_clk_class_init,
+};
+
+static void cv1800b_clk_register_types(void)
+{
+    type_register_static(&cv1800b_clk_info);
+}
+
+type_init(cv1800b_clk_register_types)
diff --git a/hw/misc/meson.build b/hw/misc/meson.build
index 245ab9b98c..a4c5f90cd8 100644
--- a/hw/misc/meson.build
+++ b/hw/misc/meson.build
@@ -35,6 +35,7 @@ system_ss.add(when: 'CONFIG_SIFIVE_E_PRCI', if_true: files('sifive_e_prci.c'))
 system_ss.add(when: 'CONFIG_SIFIVE_E_AON', if_true: files('sifive_e_aon.c'))
 system_ss.add(when: 'CONFIG_SIFIVE_U_OTP', if_true: files('sifive_u_otp.c'))
 system_ss.add(when: 'CONFIG_SIFIVE_U_PRCI', if_true: files('sifive_u_prci.c'))
+system_ss.add(when: 'CONFIG_SOPHGO_CV1800B_CLK', if_true: files('cv1800b_clk.c'))
 
 subdir('macio')
 
diff --git a/include/hw/misc/cv1800b_clk.h b/include/hw/misc/cv1800b_clk.h
new file mode 100644
index 0000000000..05c0d1ca1b
--- /dev/null
+++ b/include/hw/misc/cv1800b_clk.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Sophgo CV1800B Clock Controller
+ *
+ * Copyright (c) 2026 Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#ifndef HW_MISC_CV1800B_CLK_H
+#define HW_MISC_CV1800B_CLK_H
+
+#include "hw/core/sysbus.h"
+#include "qom/object.h"
+
+#define TYPE_CV1800B_CLK "cv1800b-clk"
+OBJECT_DECLARE_SIMPLE_TYPE(CV1800BClkState, CV1800B_CLK)
+
+struct CV1800BClkState {
+    SysBusDevice parent_obj;
+
+    MemoryRegion iomem;
+    uint32_t regs[0x1000 / 4];
+};
+
+#endif
-- 
2.54.0.563.g4f69b47b94-goog