[PATCH] hw: gpio: introduce pcf8574 driver

[Dmitriy Sharikhin <d.sharikhin@yadro.com>]

NXP PCF8574 and compatible ICs are simple I2C GPIO expanders.
PCF8574 incorporates quasi-bidirectional IO, and simple
communication protocol, when IO read is I2C byte read, and
IO write is I2C byte write. User can think of it as
open-drain port, when line high state is input and line low
state is output.

This patch allow to instantiate virtual I2C device called
"pcf8574" in machine init code via generic mechanism.

Signed-off-by: Dmitrii Sharikhin <d.sharikhin@yadro.com>
---
 hw/gpio/Kconfig           |   4 ++
 hw/gpio/meson.build       |   1 +
 hw/gpio/pcf8574.c         | 139 ++++++++++++++++++++++++++++++++++++++
 include/hw/gpio/pcf8574.h |  15 ++++
 4 files changed, 159 insertions(+)
 create mode 100644 hw/gpio/pcf8574.c
 create mode 100644 include/hw/gpio/pcf8574.h

diff --git a/hw/gpio/Kconfig b/hw/gpio/Kconfig
index d2cf3accc8..bb731ff4ce 100644
--- a/hw/gpio/Kconfig
+++ b/hw/gpio/Kconfig
@@ -16,3 +16,7 @@ config GPIO_PWR
 
 config SIFIVE_GPIO
     bool
+
+config PCF8574
+    bool
+    depends on I2C
diff --git a/hw/gpio/meson.build b/hw/gpio/meson.build
index 8a8d03d885..c0d9a3c757 100644
--- a/hw/gpio/meson.build
+++ b/hw/gpio/meson.build
@@ -15,3 +15,4 @@ system_ss.add(when: 'CONFIG_RASPI', if_true: files(
 ))
 system_ss.add(when: 'CONFIG_ASPEED_SOC', if_true: files('aspeed_gpio.c'))
 system_ss.add(when: 'CONFIG_SIFIVE_GPIO', if_true: files('sifive_gpio.c'))
+system_ss.add(when: 'CONFIG_PCF8574', if_true: files('pcf8574.c'))
diff --git a/hw/gpio/pcf8574.c b/hw/gpio/pcf8574.c
new file mode 100644
index 0000000000..a6c6bd36fa
--- /dev/null
+++ b/hw/gpio/pcf8574.c
@@ -0,0 +1,139 @@
+/*
+ * NXP PCF8574 8-port I2C GPIO expansion chip.
+ *
+ * Copyright (c) 2024 KNS Group (YADRO).
+ * Written by Dmitrii Sharikhin <d.sharikhin@yadro.com>
+ *
+ * This file is licensed under GNU GPL.
+ */
+
+#include "qemu/osdep.h"
+#include "hw/i2c/i2c.h"
+#include "hw/gpio/pcf8574.h"
+#include "hw/irq.h"
+#include "migration/vmstate.h"
+#include "qemu/log.h"
+#include "qemu/module.h"
+#include "qom/object.h"
+
+/**
+ * PCF8574 and compatible chips incorporate quasi-bidirectional
+ * IO. Electrically it means that device sustain pull-up to line
+ * unless IO port is configured as output _and_ driven low.
+ * 
+ * IO access is implemented as simple I2C single-byte read
+ * or write operation. So, to configure line to input user write 1
+ * to corresponding bit. To configure line to output and drive it low
+ * user write 0 to corresponding bit.
+ * 
+ * In essence, user can think of quasi-bidirectional IO as
+ * open-drain line, except presence of builtin rising edge acceleration
+ * embedded in PCF8574 IC
+ **/
+
+OBJECT_DECLARE_SIMPLE_TYPE(PCF8574State, PCF8574)
+
+struct PCF8574State {
+    I2CSlave parent_obj;
+    uint8_t  input;      /* external electrical line state */
+    uint8_t  output;     /* Pull-up (1) or drive low (0) on bit */
+    qemu_irq handler[8];
+    qemu_irq *gpio_in;
+};
+
+static void pcf8574_reset(DeviceState *dev)
+{
+    PCF8574State *s = PCF8574(dev);
+    s->input  = 0xFF;
+    s->output = 0xFF;
+}
+
+static inline uint8_t pcf8574_line_state(PCF8574State *s)
+{
+    // we driving line low or external circuit does that
+    return s->input & s->output; 
+}
+
+static uint8_t pcf8574_rx(I2CSlave *i2c)
+{
+    return pcf8574_line_state(PCF8574(i2c));
+}
+
+static int pcf8574_tx(I2CSlave *i2c, uint8_t data)
+{
+    PCF8574State *s = PCF8574(i2c);
+    uint8_t prev;
+    uint8_t diff;
+    uint8_t actual;
+    int line = 0;
+
+    prev = pcf8574_line_state(s);
+    s->output = data;
+    actual = pcf8574_line_state(s);
+
+    for (diff = (actual ^ prev); diff; diff &= ~(1 << line))
+    {
+        line = ctz32(diff);
+        if (s->handler[line])
+            qemu_set_irq(s->handler[line], (actual >> line) & 1);
+    }
+
+    return 0;
+}
+
+static const VMStateDescription vmstate_pcf8574 = {
+    .name = "pcf8574",
+    .version_id = 0,
+    .minimum_version_id = 0,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT8(input,  PCF8574State),
+        VMSTATE_UINT8(output, PCF8574State),
+        VMSTATE_I2C_SLAVE(parent_obj, PCF8574State),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void pcf8574_gpio_set(void *opaque, int line, int level)
+{
+    PCF8574State *s = (PCF8574State *) opaque;
+    assert(line >= 0 && line < ARRAY_SIZE(s->handler)); 
+
+    if (level)
+        s->input |=  (1 << line);
+    else
+        s->input &= ~(1 << line);
+}
+
+static void pcf8574_realize(DeviceState *dev, Error **errp)
+{
+    PCF8574State *s = PCF8574(dev);
+
+    qdev_init_gpio_in(dev, pcf8574_gpio_set, ARRAY_SIZE(s->handler));
+    qdev_init_gpio_out(dev, s->handler, ARRAY_SIZE(s->handler));
+}
+
+static void pcf8574_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass   *dc = DEVICE_CLASS(klass);
+    I2CSlaveClass *k  = I2C_SLAVE_CLASS(klass);
+
+    k->recv     = pcf8574_rx;
+    k->send     = pcf8574_tx;
+    dc->realize = pcf8574_realize;
+    dc->reset   = pcf8574_reset;
+    dc->vmsd    = &vmstate_pcf8574;
+}
+
+static const TypeInfo pcf8574_info = {
+    .name          = TYPE_PCF8574,
+    .parent        = TYPE_I2C_SLAVE,
+    .instance_size = sizeof(PCF8574State),
+    .class_init    = pcf8574_class_init,
+};
+
+static void pcf8574_register_types(void)
+{
+    type_register_static(&pcf8574_info);
+}
+
+type_init(pcf8574_register_types)
diff --git a/include/hw/gpio/pcf8574.h b/include/hw/gpio/pcf8574.h
new file mode 100644
index 0000000000..c690e73487
--- /dev/null
+++ b/include/hw/gpio/pcf8574.h
@@ -0,0 +1,15 @@
+/*
+ * NXP PCF8574 8-port I2C GPIO expansion chip.
+ *
+ * Copyright (c) 2024 KNS Group (YADRO).
+ * Written by Dmitrii Sharikhin <d.sharikhin@yadro.com>
+ *
+ * This file is licensed under GNU GPL.
+ */
+
+#ifndef _HW_GPIO_PCF8574
+#define _HW_GPIO_PCF8574
+
+#define TYPE_PCF8574 "pcf8574"
+
+#endif /* _HW_GPIO_PCF8574 */
-- 
2.39.2