Re: [PATCH v7 4/7] i3c: master: add mastership handover support

Boris Brezillon
2020-05-11T16:38:36Z

On Mon, 11 May 2020 15:14:49 +0200
Parshuram Thombare <pthombar@cadence.com> wrote:

> Added mastership acquire and yield functions.
>
> Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
> ---
> drivers/i3c/master.c | 187 +++++++++++++++++++++++++++++++++++--
> include/linux/i3c/master.h | 23 +++++
> 2 files changed, 201 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index 669bd7e45810..9c8250a6a2b0 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -16,6 +16,7 @@
> #include <linux/slab.h>
> #include <linux/spinlock.h>
> #include <linux/workqueue.h>
> +#include <linux/iopoll.h>
>
> #include "internals.h"
>
> @@ -467,6 +468,79 @@ static const char * const i3c_bus_mode_strings[] = {
> [I3C_BUS_MODE_MIXED_SLOW] = "mixed-slow",
> };
>
> +static int i3c_master_enable_mr_events(struct i3c_master_controller *master)
> +{
> + int ret;
> +
> + master->ops->enable_mr_events(master);
> + i3c_bus_maintenance_lock(&master->bus);
> + ret = i3c_master_enec_locked(master, I3C_BROADCAST_ADDR,
> + I3C_CCC_EVENT_MR | I3C_CCC_EVENT_HJ);
> + i3c_bus_maintenance_unlock(&master->bus);
> +
> + return ret;
> +}
> +
> +static int check_event_da_update(struct i3c_master_controller *m)
> +{
> + return m->ops->check_event_set(m, I3C_SLV_DA_UPDATE);
> +}
> +
> +static int check_event_mr_done(struct i3c_master_controller *m)
> +{
> + return m->ops->check_event_set(m, I3C_SLV_MR_DONE);
> +}
> +
> +/**
> + * i3c_master_acquire_bus() - acquire I3C bus mastership
> + * @m: I3C master object
> + *
> + * This function may sleep.
> + * It is expected to be called with normaluse_lock.
> + */
> +static int i3c_master_acquire_bus(struct i3c_master_controller *m)
> +{
> + int ret = 0;
> + u32 val;
> +
> + /*
> + * Request mastership needs maintenance(write) lock. So, to avoid
> + * deadlock, release normaluse(read) lock, which is expected to be
> + * held before calling this function.
> + * normaluse(read) lock is expected to be held before calling
> + * this function to avoid race with maintenance activities
> + * like DEFSLVS processing etc
> + */
> + i3c_bus_normaluse_unlock(&m->bus);
> + i3c_bus_maintenance_lock(&m->bus);
> +
> + if (m->this && m->this == m->bus.cur_master) {
> + i3c_master_disec_locked(m, I3C_BROADCAST_ADDR,
> + I3C_CCC_EVENT_MR |
> + I3C_CCC_EVENT_HJ);
> + goto mr_req_done;
> + }
> +
> + ret = readx_poll_timeout(check_event_da_update, m, val,
> + val, 100, 1000000);
> + if (ret)
> + goto mr_req_done;
> +
> + ret = m->ops->request_mastership(m);
> + if (ret)
> + goto mr_req_done;
> +
> + ret = readx_poll_timeout(check_event_mr_done, m, val,
> + val, 100, 1000000);

Those waits should be done in the master driver. Pass a timeout to
->request_master() or make it a property of the i3c_master_controller
if you like, but don't poll the status from the core.

> + if (!ret)
> + m->bus.cur_master = m->this;
> +
> +mr_req_done:
> + i3c_bus_maintenance_unlock(&m->bus);
> + i3c_bus_normaluse_lock(&m->bus);

You should downgrade the lock instead of releasing it. I really need to
get my head around this locking scheme because I'm pretty sure we had
good reasons for the locking/unlocking dance Przemek had in his series.

> + return ret;
> +}
> +
> static ssize_t mode_show(struct device *dev,
> struct device_attribute *da,
> char *buf)
> @@ -685,6 +759,33 @@ static int i3c_master_send_ccc_cmd_locked(struct i3c_master_controller *master,
> return 0;
> }
>
> +static int i3c_master_get_accmst_locked(struct i3c_master_controller *master,
> + u8 addr)
> +{
> + struct i3c_ccc_getaccmst *accmst;
> + struct i3c_ccc_cmd_dest dest;
> + struct i3c_ccc_cmd cmd;
> + int ret;
> +
> + accmst = i3c_ccc_cmd_dest_init(&dest, addr, sizeof(*accmst));
> + if (!accmst)
> + return -ENOMEM;
> +
> + i3c_ccc_cmd_init(&cmd, true, I3C_CCC_GETACCMST, &dest, 1);
> +
> + ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
> + if (ret)
> + goto out;
> +
> + if (dest.payload.len != sizeof(*accmst))
> + ret = -EIO;
> +
> +out:
> + i3c_ccc_cmd_dest_cleanup(&dest);
> +
> + return ret;
> +}
> +
> static struct i2c_dev_desc *
> i3c_master_find_i2c_dev_by_addr(const struct i3c_master_controller *master,
> u16 addr)
> @@ -1558,10 +1659,6 @@ int i3c_master_set_info(struct i3c_master_controller *master,
> if (!i3c_bus_dev_addr_is_avail(&master->bus, info->dyn_addr))
> return -EINVAL;
>
> - if (I3C_BCR_DEVICE_ROLE(info->bcr) == I3C_BCR_I3C_MASTER &&
> - master->secondary)
> - return -EINVAL;
> -
> if (master->this)
> return -EINVAL;
>
> @@ -1570,7 +1667,9 @@ int i3c_master_set_info(struct i3c_master_controller *master,
> return PTR_ERR(i3cdev);
>
> master->this = i3cdev;
> - master->bus.cur_master = master->this;
> +
> + if (!master->secondary)
> + master->bus.cur_master = master->this;

This change doesn't seem related to this patch. Looks like this should
instead go to patch 3.

>
> ret = i3c_master_attach_i3c_dev(master, i3cdev);
> if (ret)
> @@ -1612,6 +1711,73 @@ static void i3c_master_detach_free_devs(struct i3c_master_controller *master)
> }
> }
>
> +/**
> + * i3c_master_yield_bus() - yield I3C bus mastership
> + * @m: I3C master object
> + * @sec_mst_dyn_addr: address of device requesting mastership
> + *
> + * This function may sleep.
> + * It is expected to be called with normaluse_lock.
> + */
> +void
> +i3c_master_yield_bus(struct i3c_master_controller *m, u8 sec_mst_dyn_addr)
> +{
> + struct i3c_dev_desc *i3cdev;
> + int ret = 0;
> +
> + i3c_bus_maintenance_lock(&m->bus);
> + if (m->this != m->bus.cur_master)
> + goto mr_yield_done;
> +
> + /*
> + * Maintenance lock and master check above is used to
> + * avoid race amongst devices sending MR requests
> + * at the same time, as soon as ENEC MST is sent by the current
> + * master. It ensure that only one MR request is processed,
> + * rest MR requests on losing devices will timeout in wait MR
> + * DONE state. And next MR requests are blocked due to DISEC MST
> + * sent by current master in yield operation.
> + * New master should send ENEC MST once it's work is done.
> + * maintainanace lock is also needed for i3c_master_get_accmst_locked.
> + */
> +
> + ret = i3c_master_disec_locked(m, I3C_BROADCAST_ADDR,
> + I3C_CCC_EVENT_MR |
> + I3C_CCC_EVENT_HJ);

Isn't it taken care of at the controller level? I'm fine sending it
here, but I suspect some controllers might actually auto-disable MRs
once they receive one.

> + /*
> + * Once mastership is given to the new master, it is expected that
> + * MR is disabled prior to that and new master is responsible to
> + * enable it by broadcasting ENEC MR when it's work is done.
> + * If DISEC MR fails and we still go ahead with handover, chances
> + * are new master will get interrupted by unexpected MR requests.
> + */
> + if (ret)
> + goto mr_yield_done;
> +
> + ret = i3c_master_get_accmst_locked(m, sec_mst_dyn_addr);
> + if (ret)
> + goto mr_yield_done;
> +
> + i3c_bus_for_each_i3cdev(&m->bus, i3cdev) {
> + if (sec_mst_dyn_addr == i3cdev->info.dyn_addr) {
> + m->bus.cur_master = i3cdev;
> + break;
> + }
> + }
> +
> + /* Requesting device not found on i3c list. This should never happen. */
> + if (m->this == m->bus.cur_master) {

if (WARN_ON(m->this == m->bus.cur_master)) {

And you should probably check that before send DISEC.

> + ret = -EAGAIN;
> + WARN_ON(1);
> + }
> +
> +mr_yield_done:
> + i3c_bus_maintenance_unlock(&m->bus);
> + if (ret)
> + i3c_master_enable_mr_events(m);
> +}
> +EXPORT_SYMBOL_GPL(i3c_master_yield_bus);
> +
> /**
> * i3c_master_bus_init() - initialize an I3C bus
> * @master: main master initializing the bus
> @@ -2472,6 +2638,10 @@ static int i3c_master_check_ops(const struct i3c_master_controller_ops *ops)
> !ops->recycle_ibi_slot))
> return -EINVAL;
>
> + if (ops->request_mastership &&
> + (!ops->enable_mr_events || !ops->check_event_set))
> + return -EINVAL;
> +
> return 0;
> }
>
> @@ -2485,10 +2655,6 @@ static int i3c_master_init(struct i3c_master_controller *master,
> struct i2c_dev_boardinfo *i2cbi;
> int ret;
>
> - /* We do not support secondary masters yet. */
> - if (secondary)
> - return -ENOTSUPP;
> -
> ret = i3c_master_check_ops(ops);
> if (ret)
> return ret;
> @@ -2608,6 +2774,9 @@ int i3c_master_register(struct i3c_master_controller *master,
> i3c_master_register_new_i3c_devs(master);
> i3c_bus_normaluse_unlock(&master->bus);
>
> + if (ops->request_mastership)
> + ret = i3c_master_enable_mr_events(master);
> +
> return 0;
>
> err_del_dev:
> diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
> index 5124ff4831eb..dd67497ad8b1 100644
> --- a/include/linux/i3c/master.h
> +++ b/include/linux/i3c/master.h
> @@ -259,6 +259,16 @@ enum i3c_bus_mode {
> I3C_BUS_MODE_MIXED_SLOW,
> };
>
> +/**
> + * enum i3c_event - I3C master (currently acting as a slave) controller events
> + * @I3C_SLV_DA_UPDATE: I3C master has dynamic address
> + * @I3C_SLV_MR_DONE: I3C mastership request completed successfully
> + */
> +enum i3c_event {
> + I3C_SLV_DA_UPDATE,
> + I3C_SLV_MR_DONE,
> +};
> +
> /**
> * enum i3c_addr_slot_status - I3C address slot status
> * @I3C_ADDR_SLOT_FREE: address is free
> @@ -418,6 +428,12 @@ struct i3c_bus {
> * for a future IBI
> * This method is mandatory only if ->request_ibi is not
> * NULL.
> + * @request_mastership: send mastership request to the current master
> + * @enable_mr_events: enable mastership request handling by the controller
> + * @check_event_set: check events (enum i3c_event) such as device has dynamic
> + * address, mastership request is completed successfully.
> + * @sec_mst_dyn_addr: read current dynamic address of the I3C device from
> + * hardware.
> */
> struct i3c_master_controller_ops {
> int (*bus_init)(struct i3c_master_controller *master);
> @@ -445,6 +461,11 @@ struct i3c_master_controller_ops {
> int (*disable_ibi)(struct i3c_dev_desc *dev);
> void (*recycle_ibi_slot)(struct i3c_dev_desc *dev,
> struct i3c_ibi_slot *slot);
> + int (*request_mastership)(struct i3c_master_controller *master);
> + void (*enable_mr_events)(struct i3c_master_controller *m);

Those 2 helper sound good.

> + bool (*check_event_set)(struct i3c_master_controller *m,
> + enum i3c_event);
> + int (*sec_mst_dyn_addr)(struct i3c_master_controller *m);

I feel like this is HW-specific. I would just hide that in the driver
mastership-handover/DA-assignment handling. If we see enough
similarities in how other hardware handle those sequences we might want
to revise that, but I think it's a bit premature.

> };
>
> /**
> @@ -510,6 +531,8 @@ struct i3c_master_controller {
> #define i3c_bus_for_each_i3cdev(bus, dev) \
> list_for_each_entry(dev, &(bus)->devs.i3c, common.node)
>
> +void i3c_master_yield_bus(struct i3c_master_controller *m,
> + u8 sec_mst_dyn_addr);
> int i3c_master_do_i2c_xfers(struct i3c_master_controller *master,
> const struct i2c_msg *xfers,
> int nxfers);