On Thu, 26 May 2022 at 20:53, Eddie James <eajames@xxxxxxxxxxxxx> wrote:
Some I2C clients need the ability to control the root I2C bus even if theI think this looks okay. It was hard to understand at first, but makes
endpoint device is behind a mux. For example, a driver for a chip that
can't handle any I2C traffic on the bus while coming out of reset
(including an I2C-driven mux switching channels) may need to lock the root
bus with the mux selection fixed for the entire time the device is in
reset.
For this purpose, add a new structure containing two function pointers to
the adapter structure. These functions pointers should be defined for
every adapter. The lock_select operation, for a mux adapter, locks the
parent adpaters up to the root and selects the adapter's channel. The
unlock_deselect operation deselects the mux channel and unlocks all the
adapters. For a non-mux adapter, the operations lock and unlock the
adapters up to the root. This scheme should work with multiple levels of
muxes and regular adapters in between.
Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>
more sense with the context of the existing bus locking code.
There's a typo in one of your comments that the 0day bot found.
Have you tested with CONFIG_DEBUG_MUTEXES?
Reviewed-by: Joel Stanley <joel@xxxxxxxxx>
---Recursive lock the set of adaptors.
drivers/i2c/i2c-core-base.c | 38 ++++++++++++++++++++++++++++
drivers/i2c/i2c-mux.c | 50 +++++++++++++++++++++++++++++++++++++
include/linux/i2c.h | 42 +++++++++++++++++++++++++++++++
3 files changed, 130 insertions(+)
diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index d43db2c3876e..e2c365348e1f 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1357,6 +1357,41 @@ static const struct i2c_lock_operations i2c_adapter_lock_ops = {
.unlock_bus = i2c_adapter_unlock_bus,
};
+/*
+ * For a non-mux adapter, the lock_select operation locks the chain of
+ * adapters upwards, returning the root. If there's a mux above this adapter
+ * somehow, it should also get locked and the desired channel selected.
+ */
+static struct i2c_adapter *i2c_adapter_lock_select(struct i2c_adapter *adapter)
+{
+ struct i2c_adapter *ret = adapter;
+ struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
+
+ if (parent) {
+ ret = parent->mux_root_ops->lock_select(parent);
+ if (IS_ERR(ret))
+ return ret;
+ }
+
+ adapter->lock_ops->lock_bus(adapter, I2C_LOCK_ROOT_ADAPTER);
+ return ret;
+}
+
+static void i2c_adapter_unlock_deselect(struct i2c_adapter *adapter)
+{
+ struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
+
+ adapter->lock_ops->unlock_bus(adapter, I2C_LOCK_ROOT_ADAPTER);
+
+ if (parent)
+ parent->mux_root_ops->unlock_deselect(parent);
+}
+
+static const struct i2c_mux_root_operations i2c_adapter_mux_root_ops = {
+ .lock_select = i2c_adapter_lock_select,
+ .unlock_deselect = i2c_adapter_unlock_deselect,
+};
+
static void i2c_host_notify_irq_teardown(struct i2c_adapter *adap)
{
struct irq_domain *domain = adap->host_notify_domain;
@@ -1452,6 +1487,9 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
if (!adap->lock_ops)
adap->lock_ops = &i2c_adapter_lock_ops;
+ if (!adap->mux_root_ops)
+ adap->mux_root_ops = &i2c_adapter_mux_root_ops;
+
adap->locked_flags = 0;
rt_mutex_init(&adap->bus_lock);
rt_mutex_init(&adap->mux_lock);
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 774507b54b57..c7db770e4198 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -210,6 +210,49 @@ static void i2c_parent_unlock_bus(struct i2c_adapter *adapter,
rt_mutex_unlock(&parent->mux_lock);
}
+/*
+ * For a mux adapter, the lock_select operation first locks just like the
+ * lock_bus operation. Then it selects the channel for this adapter and
+ * returns the root adapter. If there is another mux above this one, calling
+ * the parent lock_select should ensure that the channel is correctly
+ * selected.
+ */
+static struct i2c_adapter *i2c_mux_lock_select(struct i2c_adapter *adapter)
+{
+ int ret;
+ struct i2c_mux_priv *priv = adapter->algo_data;
+ struct i2c_mux_core *muxc = priv->muxc;
+ struct i2c_adapter *parent = muxc->parent;
+
+ rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
+
+ adapter = parent->mux_root_ops->lock_select(parent);
+ if (IS_ERR(adapter))
+ return adapter;
+
+ ret = muxc->select(muxc, priv->chan_id);
+ if (ret < 0) {
+ parent->mux_root_ops->unlock_deselect(parent);
+ rt_mutex_unlock(&parent->mux_lock);
+ return ERR_PTR(ret);
+ }
+
+ return adapter;
+}
+
+static void i2c_mux_unlock_deselect(struct i2c_adapter *adapter)
+{
+ struct i2c_mux_priv *priv = adapter->algo_data;
+ struct i2c_mux_core *muxc = priv->muxc;
+ struct i2c_adapter *parent = muxc->parent;
+
+ if (muxc->deselect)
+ muxc->deselect(muxc, priv->chan_id);
+
+ parent->mux_root_ops->unlock_deselect(parent);
+ rt_mutex_unlock(&parent->mux_lock);
+}
+
struct i2c_adapter *i2c_root_adapter(struct device *dev)
{
struct device *i2c;
@@ -279,6 +322,11 @@ static const struct i2c_lock_operations i2c_parent_lock_ops = {
.unlock_bus = i2c_parent_unlock_bus,
};
+static const struct i2c_mux_root_operations i2c_mux_root_ops = {
+ .lock_select = i2c_mux_lock_select,
+ .unlock_deselect = i2c_mux_unlock_deselect,
+};
+
int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
u32 force_nr, u32 chan_id,
unsigned int class)
@@ -339,6 +387,8 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
else
priv->adap.lock_ops = &i2c_parent_lock_ops;
+ priv->adap.mux_root_ops = &i2c_mux_root_ops;
+
/* Sanity check on class */
if (i2c_mux_parent_classes(parent) & class)
dev_err(&parent->dev,
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index fbda5ada2afc..a3596f61b417 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -583,6 +583,26 @@ struct i2c_lock_operations {
void (*unlock_bus)(struct i2c_adapter *adapter, unsigned int flags);
};
+/**
+ * struct i2c_mux_root_operations - represent operations to lock and select
+ * the adapter's mux channel (if a mux is present)
+ * @lock_select: Get exclusive access to the root I2C bus adapter with the
+ * correct mux channel selected for the adapter
+ * @unlock_deslect: Release exclusive access to the root I2C bus adapter and
+ * deselect the mux channel for the adapter
+ *
+ * Some I2C clients need the ability to control the root I2C bus even if the
+ * endpoint device is behind a mux. For example, a driver for a chip that
+ * can't handle any I2C traffic on the bus while coming out of reset (including
+ * an I2C-driven mux switching channels) may need to lock the root bus with
+ * the mux selection fixed for the entire time the device is in reset.
+ * These operations are for such a purpose.
+ */
+struct i2c_mux_root_operations {
+ struct i2c_adapter *(*lock_select)(struct i2c_adapter *adapter);
+ void (*unlock_deselect)(struct i2c_adapter *adapter);
+};
+
/**
* struct i2c_timings - I2C timing information
* @bus_freq_hz: the bus frequency in Hz
@@ -725,6 +745,7 @@ struct i2c_adapter {
/* data fields that are valid for all devices */
const struct i2c_lock_operations *lock_ops;
+ const struct i2c_mux_root_operations *mux_root_ops;
struct rt_mutex bus_lock;
struct rt_mutex mux_lock;
@@ -817,6 +838,27 @@ i2c_unlock_bus(struct i2c_adapter *adapter, unsigned int flags)
adapter->lock_ops->unlock_bus(adapter, flags);
}
+/**
+ * i2c_lock_select_bus - Get exclusive access to the root I2C bus with the
+ * target's mux channel (if a mux is present) selected.
+ * @adapter: Target I2C bus
+ *
+ * Return the root I2C bus if mux selection succeeds, an ERR_PTR otherwise
+ */
+static inline struct i2c_adapter *i2c_lock_select_bus(struct i2c_adapter *adapter)
+{
+ return adapter->mux_root_ops->lock_select(adapter);
+}
+
+/**
+ * i2c_unlock_deslect_bus - Release exclusive access to the root I2C bus
+ * @adapter: Target I2C bus
+ */
+static inline void i2c_unlock_deselect_bus(struct i2c_adapter *adapter)
+{
+ adapter->mux_root_ops->unlock_deselect(adapter);
+}
+
/**
* i2c_mark_adapter_suspended - Report suspended state of the adapter to the core
* @adap: Adapter to mark as suspended
--
2.27.0