Re: [PATCH v2 4/4] hw/i2c: add pca954x i2c-mux switch

[Corey Minyard]

On Fri, Apr 09, 2021 at 09:25:45AM -0700, Patrick Venture wrote:
> The pca954x is an i2c mux, and this adds support for two variants of
> this device: the pca9546 and pca9548.
> 
> This device is very common on BMCs to route a different channel to each
> PCIe i2c bus downstream from the BMC.
> 
> Signed-off-by: Patrick Venture <venture@google.com>
> Reviewed-by: Hao Wu <wuhaotsh@google.com>
> Reviewed-by: Havard Skinnemoen <hskinnemoen@google.com>
> ---
>  MAINTAINERS                      |   6 +
>  hw/i2c/Kconfig                   |   4 +
>  hw/i2c/i2c_mux_pca954x.c         | 290 +++++++++++++++++++++++++++++++
>  hw/i2c/meson.build               |   1 +
>  hw/i2c/trace-events              |   5 +
>  include/hw/i2c/i2c_mux_pca954x.h |  19 ++
>  6 files changed, 325 insertions(+)
>  create mode 100644 hw/i2c/i2c_mux_pca954x.c
>  create mode 100644 include/hw/i2c/i2c_mux_pca954x.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 58f342108e..5ea0b60b8a 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2039,6 +2039,12 @@ S: Maintained
>  F: hw/net/tulip.c
>  F: hw/net/tulip.h
>  
> +pca954x
> +M: Patrick Venture <venture@google.com>
> +S: Maintained
> +F: hw/i2c/i2c_mux_pca954x.c
> +F: include/hw/i2c/i2c_mux_pca954x.h
> +
>  Generic Loader
>  M: Alistair Francis <alistair@alistair23.me>
>  S: Maintained
> diff --git a/hw/i2c/Kconfig b/hw/i2c/Kconfig
> index 09642a6dcb..8d120a25d5 100644
> --- a/hw/i2c/Kconfig
> +++ b/hw/i2c/Kconfig
> @@ -28,3 +28,7 @@ config IMX_I2C
>  config MPC_I2C
>      bool
>      select I2C
> +
> +config PCA954X
> +    bool
> +    select I2C
> diff --git a/hw/i2c/i2c_mux_pca954x.c b/hw/i2c/i2c_mux_pca954x.c
> new file mode 100644
> index 0000000000..9aa1a8872f
> --- /dev/null
> +++ b/hw/i2c/i2c_mux_pca954x.c
> @@ -0,0 +1,290 @@
> +/*
> + * I2C multiplexer for PCA954x series of I2C multiplexer/switch chips.
> + *
> + * Copyright 2021 Google LLC
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful, but 
> WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
> + * for more details.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "hw/i2c/i2c.h"
> +#include "hw/i2c/i2c_mux_pca954x.h"
> +#include "hw/i2c/smbus_slave.h"
> +#include "hw/qdev-core.h"
> +#include "hw/sysbus.h"
> +#include "qemu/log.h"
> +#include "qemu/module.h"
> +#include "qemu/queue.h"
> +#include "qom/object.h"
> +#include "trace.h"
> +
> +#define PCA9548_CHANNEL_COUNT 8
> +#define PCA9546_CHANNEL_COUNT 4
> +
> +/*
> + * struct Pca954xChannel - The i2c mux device will have N of these states
> + * that own the i2c channel bus.
> + * @bus: The owned channel bus.
> + * @enabled: Is this channel active?
> + */
> +typedef struct Pca954xChannel {
> +    SysBusDevice parent;
> +
> +    I2CBus       *bus;
> +
> +    bool         enabled;
> +} Pca954xChannel;
> +
> +#define TYPE_PCA954X_CHANNEL "pca954x-channel"
> +#define PCA954X_CHANNEL(obj) \
> +    OBJECT_CHECK(Pca954xChannel, (obj), TYPE_PCA954X_CHANNEL)
> +
> +/*
> + * struct Pca954xState - The pca954x state object.
> + * @control: The value written to the mux control.
> + * @channel: The set of i2c channel buses that act as channels which own the
> + * i2c children.
> + */
> +typedef struct Pca954xState {
> +    SMBusDevice parent;
> +
> +    uint8_t control;
> +
> +    /* The channel i2c buses. */
> +    Pca954xChannel channel[PCA9548_CHANNEL_COUNT];
> +} Pca954xState;
> +
> +/*
> + * struct Pca954xClass - The pca954x class object.
> + * @nchans: The number of i2c channels this device has.
> + */
> +typedef struct Pca954xClass {
> +    SMBusDeviceClass parent;
> +
> +    uint8_t nchans;
> +} Pca954xClass;
> +
> +#define TYPE_PCA954X "pca954x"
> +OBJECT_DECLARE_TYPE(Pca954xState, Pca954xClass, PCA954X)
> +
> +/*
> + * For each channel, if it's enabled, recursively call match on those 
> children.
> + */
> +static bool pca954x_match(I2CSlave *candidate, uint8_t address,
> +                          bool broadcast,
> +                          I2CNodeList *current_devs)
> +{
> +    Pca954xState *mux = PCA954X(candidate);
> +    Pca954xClass *mc = PCA954X_GET_CLASS(mux);
> +    int i;
> +
> +    /* They are talking to the mux itself (or all devices enabled. */

Missing close paren in the comment above.  Really minor nit :)

> +    if ((candidate->address == address) || broadcast) {
> +        I2CNode *node = g_malloc(sizeof(struct I2CNode));
> +        node->elt = candidate;
> +        QLIST_INSERT_HEAD(current_devs, node, next);
> +        if (!broadcast) {
> +            return true;
> +        }
> +    }
> +
> +    for (i = 0; i < mc->nchans; i++) {
> +        if (!mux->channel[i].enabled) {
> +            continue;
> +        }
> +
> +        if (i2c_scan_bus(mux->channel[i].bus, address, broadcast)) {
> +            if (!broadcast) {
> +                return true;
> +            }
> +        }
> +    }
> +
> +    /* If we arrived here we didn't find a match, return broadcast. */
> +    return broadcast;
> +}
> +
> +static void pca954x_enable_channel(Pca954xState *s, uint8_t enable_mask)
> +{
> +    Pca954xClass *mc = PCA954X_GET_CLASS(s);
> +    int i;
> +
> +    /*
> +     * For each channel, check if their bit is set in enable_mask and if yes,
> +     * enable it, otherwise disable, hide it.
> +     */
> +    for (i = 0; i < mc->nchans; i++) {
> +        if (enable_mask & (1 << i)) {
> +            s->channel[i].enabled = true;
> +        } else {
> +            s->channel[i].enabled = false;
> +        }
> +    }
> +}
> +
> +static void pca954x_write(Pca954xState *s, uint8_t data)
> +{
> +    s->control = data;
> +    pca954x_enable_channel(s, data);
> +
> +    trace_pca954x_write_bytes(data);
> +}
> +
> +static int pca954x_write_data(SMBusDevice *d, uint8_t *buf, uint8_t len)
> +{
> +    Pca954xState *s = PCA954X(d);
> +
> +    if (len == 0) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "%s: writing empty data\n", __func__);
> +        return -1;
> +    }
> +
> +    /*
> +     * len should be 1, because they write one byte to enable/disable 
> channels.
> +     */
> +    if (len > 1) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +            "%s: extra data after channel selection mask\n",
> +            __func__);
> +        return -1;
> +    }
> +
> +    pca954x_write(s, buf[0]);
> +    return 0;
> +}
> +
> +static uint8_t pca954x_read_byte(SMBusDevice *d)
> +{
> +    Pca954xState *s = PCA954X(d);
> +    uint8_t data = s->control;
> +    trace_pca954x_read_data(data);
> +    return data;
> +}
> +
> +static void pca954x_enter_reset(Object *obj, ResetType type)
> +{
> +    Pca954xState *s = PCA954X(obj);
> +    /* Reset will disable all channels. */
> +    pca954x_write(s, 0);
> +}
> +
> +I2CBus *pca954x_i2c_get_bus(I2CSlave *mux, uint8_t channel)
> +{
> +    Pca954xClass *pc = PCA954X_GET_CLASS(mux);
> +    Pca954xState *pca954x = PCA954X(mux);
> +
> +    g_assert(channel < pc->nchans);
> +    return I2C_BUS(qdev_get_child_bus(DEVICE(&pca954x->channel[channel]),
> +                                      "i2c-bus"));
> +}
> +
> +static void pca954x_smbus_init(Object *obj)
> +{
> +    Pca954xChannel *s = PCA954X_CHANNEL(obj);
> +    s->bus = i2c_init_bus(DEVICE(s), "i2c-bus");
> +
> +    /* Start all channels as disabled. */
> +    s->enabled = false;
> +}
> +
> +static void pca954x_channel_class_init(ObjectClass *klass, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +    dc->desc = "Pca954x Channel";
> +}
> +
> +static void pca9546_class_init(ObjectClass *klass, void *data)
> +{
> +    Pca954xClass *s = PCA954X_CLASS(klass);
> +    s->nchans = PCA9546_CHANNEL_COUNT;
> +}
> +
> +static void pca9548_class_init(ObjectClass *oc, void *data)
> +{
> +    Pca954xClass *s = PCA954X_CLASS(oc);
> +    s->nchans = PCA9548_CHANNEL_COUNT;
> +}
> +
> +static void pca954x_realize(DeviceState *dev, Error **errp)
> +{
> +    Pca954xState *s = PCA954X(dev);
> +    Pca954xClass *c = PCA954X_GET_CLASS(s);
> +    int i;
> +
> +    /* SMBus modules. Cannot fail. */
> +    for (i = 0; i < c->nchans; i++) {
> +        Object *obj = OBJECT(&s->channel[i]);
> +        sysbus_realize(SYS_BUS_DEVICE(obj), &error_abort);
> +    }
> +}
> +
> +static void pca954x_init(Object *obj)
> +{
> +    int i;
> +    Pca954xState *s = PCA954X(obj);
> +    Pca954xClass *c = PCA954X_GET_CLASS(obj);
> +
> +    /* Only initialize the children we expect. */
> +    for (i = 0; i < c->nchans; i++) {
> +        object_initialize_child(obj, "channel[*]", &s->channel[i],
> +                                TYPE_PCA954X_CHANNEL);
> +    }
> +}
> +
> +static void pca954x_class_init(ObjectClass *klass, void *data)
> +{
> +    I2CSlaveClass *sc = I2C_SLAVE_CLASS(klass);
> +    ResettableClass *rc = RESETTABLE_CLASS(klass);
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +    SMBusDeviceClass *k = SMBUS_DEVICE_CLASS(klass);
> +
> +    sc->match_and_add = pca954x_match;
> +
> +    rc->phases.enter = pca954x_enter_reset;
> +
> +    dc->desc = "Pca954x i2c-mux";
> +    dc->realize = pca954x_realize;
> +
> +    k->write_data = pca954x_write_data;
> +    k->receive_byte = pca954x_read_byte;
> +}
> +
> +static const TypeInfo pca954x_info[] = {
> +    {
> +        .name          = TYPE_PCA954X,
> +        .parent        = TYPE_SMBUS_DEVICE,
> +        .instance_size = sizeof(Pca954xState),
> +        .instance_init = pca954x_init,
> +        .class_size    = sizeof(Pca954xClass),
> +        .class_init    = pca954x_class_init,
> +        .abstract      = true,
> +    },
> +    {
> +        .name          = TYPE_PCA9546,
> +        .parent        = TYPE_PCA954X,
> +        .class_init    = pca9546_class_init,
> +    },
> +    {
> +        .name          = TYPE_PCA9548,
> +        .parent        = TYPE_PCA954X,
> +        .class_init    = pca9548_class_init,
> +    },
> +    {
> +        .name = TYPE_PCA954X_CHANNEL,
> +        .parent = TYPE_SYS_BUS_DEVICE,
> +        .class_init = pca954x_channel_class_init,
> +        .instance_size = sizeof(Pca954xChannel),
> +        .instance_init = pca954x_smbus_init,
> +    }
> +};
> +
> +DEFINE_TYPES(pca954x_info)
> diff --git a/hw/i2c/meson.build b/hw/i2c/meson.build
> index cdcd694a7f..dd3aef02b2 100644
> --- a/hw/i2c/meson.build
> +++ b/hw/i2c/meson.build
> @@ -14,4 +14,5 @@ i2c_ss.add(when: 'CONFIG_SMBUS_EEPROM', if_true: 
> files('smbus_eeprom.c'))
>  i2c_ss.add(when: 'CONFIG_VERSATILE_I2C', if_true: files('versatile_i2c.c'))
>  i2c_ss.add(when: 'CONFIG_OMAP', if_true: files('omap_i2c.c'))
>  i2c_ss.add(when: 'CONFIG_PPC4XX', if_true: files('ppc4xx_i2c.c'))
> +i2c_ss.add(when: 'CONFIG_PCA954X', if_true: files('i2c_mux_pca954x.c'))
>  softmmu_ss.add_all(when: 'CONFIG_I2C', if_true: i2c_ss)
> diff --git a/hw/i2c/trace-events b/hw/i2c/trace-events
> index 82fe6f965f..82f19e6a2d 100644
> --- a/hw/i2c/trace-events
> +++ b/hw/i2c/trace-events
> @@ -26,3 +26,8 @@ npcm7xx_smbus_recv_byte(const char *id, uint8_t value) "%s 
> recv byte: 0x%02x"
>  npcm7xx_smbus_stop(const char *id) "%s stopping"
>  npcm7xx_smbus_nack(const char *id) "%s nacking"
>  npcm7xx_smbus_recv_fifo(const char *id, uint8_t received, uint8_t expected) 
> "%s recv fifo: received %u, expected %u"
> +
> +# i2c-mux-pca954x.c
> +
> +pca954x_write_bytes(uint8_t value) "PCA954X write data: 0x%02x"
> +pca954x_read_data(uint8_t value) "PCA954X read data: 0x%02x"
> diff --git a/include/hw/i2c/i2c_mux_pca954x.h 
> b/include/hw/i2c/i2c_mux_pca954x.h
> new file mode 100644
> index 0000000000..8aaf9bbc39
> --- /dev/null
> +++ b/include/hw/i2c/i2c_mux_pca954x.h
> @@ -0,0 +1,19 @@
> +#ifndef QEMU_I2C_MUX_PCA954X
> +#define QEMU_I2C_MUX_PCA954X
> +
> +#include "hw/i2c/i2c.h"
> +
> +#define TYPE_PCA9546 "pca9546"
> +#define TYPE_PCA9548 "pca9548"
> +
> +/**
> + * Retrieves the i2c bus associated with the specified channel on this i2c
> + * mux.
> + * @mux: an i2c mux device.
> + * @channel: the i2c channel requested
> + *
> + * Returns: a pointer to the associated i2c bus.
> + */
> +I2CBus *pca954x_i2c_get_bus(I2CSlave *mux, uint8_t channel);

I assume your machine-specific code will be referencing this, which is
the way it should work.

I'm happy with this.

-corey

> +
> +#endif
> -- 
> 2.31.1.295.g9ea45b61b8-goog
>