[PATCH 1/7] i2c: mux: add the ability to share mux-address with child nodes

[Peter Rosin]

Hi!

2024-05-02 at 17:01, Farouk Bouabid wrote:
> Hi Peter,
> 
> On 29.04.24 17:46, Peter Rosin wrote:
>> Hi!
>>
>> 2024-04-26 at 18:49, Farouk Bouabid wrote:
>>> Allow the mux to have the same address as a child device. This is useful
>>> when the mux can only use an i2c-address that is used by a child device
>>> because no other addresses are free to use. eg. the mux can only use
>>> address 0x18 which is used by amc6821 connected to the mux.
>>>
>>> Signed-off-by: Farouk Bouabid <farouk.bouabid at theobroma-systems.com>
>>> ---
>>>   drivers/i2c/i2c-mux.c   | 10 +++++++++-
>>>   include/linux/i2c-mux.h |  1 +
>>>   2 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
>>> index 57ff09f18c37..f5357dff8cc5 100644
>>> --- a/drivers/i2c/i2c-mux.c
>>> +++ b/drivers/i2c/i2c-mux.c
>>> @@ -331,7 +331,6 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
>>>       priv->adap.owner = THIS_MODULE;
>>>       priv->adap.algo = &priv->algo;
>>>       priv->adap.algo_data = priv;
>>> -    priv->adap.dev.parent = &parent->dev;
>>>       priv->adap.retries = parent->retries;
>>>       priv->adap.timeout = parent->timeout;
>>>       priv->adap.quirks = parent->quirks;
>>> @@ -348,6 +347,15 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
>>>       else
>>>           priv->adap.class = class;
>>>   +    /*
>>> +     * When creating the adapter, the node devices are checked for i2c address
>>> +     * match with other devices on the parent adapter, among which is the mux itself.
>>> +     * If a match is found the node device is not probed successfully.
>>> +     * Allow the mux to have the same address as a child device by skipping this check.
>>> +     */
>>> +    if (!(muxc->share_addr_with_children))
>>> +        priv->adap.dev.parent = &parent->dev;
>> This is a dirty hack that will not generally do the right thing.
>>
>> The adapter device parent is not there solely for the purpose of
>> detecting address clashes, so the above has other implications
>> that are not desirable.
>>
>> Therefore, NACK on this approach. It simply needs to be more involved.
>> Sorry.
>>
>> Cheers,
>> Peter
>>
> 
> Another way to approach this is by implementing this flag as a quirk for the added adapter:
> 
> (tested but not cleaned up)

Yes, good idea, this is much more targeted and generally feels a lot
better.

> 
> """
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index ff5c486a1dbb..6a0237f750db 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -821,9 +821,21 @@ static int i2c_check_mux_children(struct device *dev, void *addrp)
>  static int i2c_check_addr_busy(struct i2c_adapter *adapter, int addr)
>  {
>         struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
> +       bool skip_check = false;
>         int result = 0;
> 
> -       if (parent)
> +       if (adapter->quirks) {
> +                if (adapter->quirks->flags & I2C_AQ_SHARE_ADDR) {
> +                       struct i2c_client *client = of_find_i2c_device_by_node(adapter->dev.of_node->parent);
> +
> +                       if (client) {
> +                               skip_check = client->addr == addr;
> +                               put_device(&client->dev);
> +                       }
> +                }
> +       }
> +
> +       if (parent && !skip_check)
>                 result = i2c_check_mux_parents(parent, addr);
> 
>         if (!result)
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> index 57ff09f18c37..e87cb0e43725 100644
> --- a/drivers/i2c/i2c-mux.c
> +++ b/drivers/i2c/i2c-mux.c
> @@ -334,7 +334,26 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
>         priv->adap.dev.parent = &parent->dev;
>         priv->adap.retries = parent->retries;
>         priv->adap.timeout = parent->timeout;
> -       priv->adap.quirks = parent->quirks;
> +       /*
> +        * When creating the adapter, the node devices are checked for i2c address
> +        * match with other devices on the parent adapter, among which is the mux itself.
> +        * If a match is found the node device is not probed successfully.
> +        * Allow the mux to have the same address as a child device by skipping this check.
> +        */
> +       if (!muxc->share_addr_with_children)
> +               priv->adap.quirks = parent->quirks;
> +       else {
> +               struct i2c_adapter_quirks *quirks = kzalloc(sizeof(*quirks), GFP_KERNEL);

This leaks, dev_kzalloc?

> +               if (!quirks)
> +                       return -ENOMEM;
> +
> +               if (parent->quirks)
> +                       *quirks = *(parent->quirks); // @fixme memcpy
> +
> +               quirks->flags |= I2C_AQ_SHARE_ADDR;
> +               priv->adap.quirks = quirks;
> +       }
> +
>         if (muxc->mux_locked)
>                 priv->adap.lock_ops = &i2c_mux_lock_ops;
>         else
> diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
> index 98ef73b7c8fd..17ac68bf1703 100644
> --- a/include/linux/i2c-mux.h
> +++ b/include/linux/i2c-mux.h
> @@ -21,6 +21,7 @@ struct i2c_mux_core {
>         unsigned int mux_locked:1;
>         unsigned int arbitrator:1;
>         unsigned int gate:1;
> +       unsigned int share_addr_with_children:1;
> 
>         void *priv;
> 
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 5e6cd43a6dbd..2ebac9e672ef 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -711,6 +711,8 @@ struct i2c_adapter_quirks {
>  #define I2C_AQ_NO_ZERO_LEN             (I2C_AQ_NO_ZERO_LEN_READ | I2C_AQ_NO_ZERO_LEN_WRITE)
>  /* adapter cannot do repeated START */
>  #define I2C_AQ_NO_REP_START            BIT(7)
> +/* @fixme document and find proper name */
> +#define I2C_AQ_SHARE_ADDR              BIT(8)
> 
>  /*
>   * i2c_adapter is the structure used to identify a physical i2c bus along
> 
> """
> 
> This works, however this only supports device-tree because of of_find_i2c_device_by_node. If we want to support acpi then we can either:
> 
> 
> 1. Get the Mule i2c device address from fwnode_get_next_parent_dev but this is static since v6.9-rcx.
> 
> 2. Pass the Mule i2c device address as a new member of  struct i2c_adapter_quirks.
> 
> 
> I would go for 2. Do you suggest something else?

Yes, 2 is definitely neater.

Thanks!

Cheers,
Peter