The pinN QOM accessors are meant to let external agents observe and stimulate the expander's pins, but their default behaviour does not match real hardware:
- to "drive" a pin, set_pin writes the OUTPUT register and then clears the pin's Configuration bit to force it into output mode. On a real device the pin direction is owned solely by the host (programmed through the Configuration register over I2C); an external agent can neither flip a pin's direction nor impose a level on a pin the host drives as an output -- the latter is a voltage conflict, not a legal operation. - get_pin returns a CONFIG|OUTPUT composite, i.e. the guest's intent, rather than the level actually sampled on the pin. The PCA9555 GPIO variant (hw/gpio/pca9552.c) already models this correctly and unconditionally: only input-configured pins can be driven from outside, and reads return the sampled INPUT register. Add a "hw-dir" property to bring the pca9554 pin accessors in line with the hardware (and with the PCA9555 model), without changing the behaviour seen by existing users: - hw-dir=true: set_pin only drives pins the guest has configured as inputs; a set on an output pin is refused with a LOG_UNIMP warning. get_pin returns the sampled INPUT register. - hw-dir=false (default): keeps the legacy, non-conformant behaviour for backward compatibility. Signed-off-by: Emmanuel Blot <[email protected]> --- hw/gpio/pca9554.c | 65 ++++++++++++++++++++++++++++++----------------- include/hw/gpio/pca9554.h | 1 + 2 files changed, 43 insertions(+), 23 deletions(-) diff --git a/hw/gpio/pca9554.c b/hw/gpio/pca9554.c index b44ec0d999..ed38fe102b 100644 --- a/hw/gpio/pca9554.c +++ b/hw/gpio/pca9554.c @@ -154,6 +154,14 @@ static int pca9554_event(I2CSlave *i2c, enum i2c_event event) return 0; } +static void pca9554_set_ext_state(PCA9554State *s, int pin, int level) +{ + if (s->ext_state[pin] != level) { + s->ext_state[pin] = level; + pca9554_update_pin_input(s); + } +} + static void pca9554_get_pin(Object *obj, Visitor *v, const char *name, void *opaque, Error **errp) { @@ -171,9 +179,13 @@ static void pca9554_get_pin(Object *obj, Visitor *v, const char *name, return; } - state = pca9554_read(s, PCA9554_CONFIG); - state |= pca9554_read(s, PCA9554_OUTPUT); - state = (state >> pin) & 0x1; + /* + * Report the physical pin level. The input register is kept in sync by + * pca9554_update_pin_input(): output pins mirror the OUTPUT register and + * input pins reflect the externally driven (or pulled-up) level, so it + * holds the wire level regardless of the configured direction. + */ + state = (s->regs[PCA9554_INPUT] >> pin) & 0x1; visit_type_str(v, name, (char **)&pin_state[state], errp); } @@ -208,20 +220,34 @@ static void pca9554_set_pin(Object *obj, Visitor *v, const char *name, return; } - /* First, modify the output register bit */ - val = pca9554_read(s, PCA9554_OUTPUT); - mask = 0x1 << pin; - if (state == PCA9554_PIN_LOW) { - val &= ~(mask); + if (s->hw_dir) { + /* Warn and ignore if the guest has configured this pin as output */ + if (!((s->regs[PCA9554_CONFIG] >> pin) & 0x1)) { + qemu_log_mask(LOG_UNIMP, + "%s: pin %d is configured as output, " + "ignoring external set\n", + s->description, pin); + return; + } + /* Drive the external input level */ + pca9554_set_ext_state(s, pin, state != PCA9554_PIN_LOW); } else { - val |= mask; - } - pca9554_write(s, PCA9554_OUTPUT, val); + /* Legacy behavior: force output mode and drive */ + /* First, modify the output register bit */ + val = pca9554_read(s, PCA9554_OUTPUT); + mask = 0x1 << pin; + if (state == PCA9554_PIN_LOW) { + val &= ~(mask); + } else { + val |= mask; + } + pca9554_write(s, PCA9554_OUTPUT, val); - /* Then, clear the config register bit for output mode */ - val = pca9554_read(s, PCA9554_CONFIG); - val &= ~mask; - pca9554_write(s, PCA9554_CONFIG, val); + /* Then, clear the config register bit for output mode */ + val = pca9554_read(s, PCA9554_CONFIG); + val &= ~mask; + pca9554_write(s, PCA9554_CONFIG, val); + } } static const VMStateDescription pca9554_vmstate = { @@ -271,14 +297,6 @@ static void pca9554_initfn(Object *obj) } } -static void pca9554_set_ext_state(PCA9554State *s, int pin, int level) -{ - if (s->ext_state[pin] != level) { - s->ext_state[pin] = level; - pca9554_update_pin_input(s); - } -} - static void pca9554_gpio_in_handler(void *opaque, int pin, int level) { PCA9554State *s = PCA9554(opaque); @@ -303,6 +321,7 @@ static void pca9554_realize(DeviceState *dev, Error **errp) static const Property pca9554_properties[] = { DEFINE_PROP_STRING("description", PCA9554State, description), + DEFINE_PROP_BOOL("hw-dir", PCA9554State, hw_dir, false), }; static void pca9554_class_init(ObjectClass *klass, const void *data) diff --git a/include/hw/gpio/pca9554.h b/include/hw/gpio/pca9554.h index c09108e8b6..ac835371aa 100644 --- a/include/hw/gpio/pca9554.h +++ b/include/hw/gpio/pca9554.h @@ -33,6 +33,7 @@ struct PCA9554State { qemu_irq gpio_out[PCA9554_PIN_COUNT]; uint8_t ext_state[PCA9554_PIN_COUNT]; char *description; /* For debugging purpose only */ + bool hw_dir; /* Honor pin direction */ }; #endif -- 2.50.1
