Messages in this thread | | | Date | Tue, 6 Sep 2022 15:10:49 -0500 | Subject | Re: [PATCH 1/2] i2c: core: Add mux root adapter operations | From | Eddie James <> |
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On 6/3/22 03:01, Joel Stanley wrote: > On Thu, 26 May 2022 at 20:53, Eddie James <eajames@linux.ibm.com> wrote: >> 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. >> 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@linux.ibm.com> > I think this looks okay. It was hard to understand at first, but makes > 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?
Getting back around to this... Yes, I just tested with CONFIG_DEBUG_MUTEXES and didn't see any issues.
I will address the comment typo in v2 now.
Thanks,
Eddie
> > Reviewed-by: Joel Stanley <joel@jms.id.au> > >> --- >> 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. >> + */ > Recursive lock the set of adaptors. > >> +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 >>
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