Re: [PATCH v2] i2c: Add generic support passing secondary devices addresses

[Mika Westerberg]

+Srinivas

On Sun, Jan 31, 2016 at 04:33:00PM +0100, Jean-Michel Hautbois wrote:
> Some I2C devices have multiple addresses assigned, for example each address
> corresponding to a different internal register map page of the device.
> So far drivers which need support for this have handled this with a driver
> specific and non-generic implementation, e.g. passing the additional address
> via platform data.
> 
> This patch provides a new helper function called i2c_new_secondary_device()
> which is intended to provide a generic way to get the secondary address
> as well as instantiate a struct i2c_client for the secondary address.
> 
> The function expects a pointer to the primary i2c_client, a name
> for the secondary address and an optional default address. The name is used
> as a handle to specify which secondary address to get.
> 
> The default address is used as a fallback in case no secondary address
> was explicitly specified. In case no secondary address and no default
> address were specified the function returns NULL.
> 
> For now the function only supports look-up of the secondary address
> from devicetree, but it can be extended in the future
> to for example support board files and/or ACPI.

It was not clear to me but does this support more than two addresses?
For example we might a device with 3 I2cSerialBus() connectors:

    Device (CAM1)
    {
        Method (_CRS, 0, NotSerialized)  // _CRS: Current Resource Settings
        {
            Name (SBUF, ResourceTemplate ()
            {
                ...
                I2cSerialBus (0x0010, ControllerInitiated, 0x00061A80,
                    AddressingMode7Bit, "\\_SB.I2C4",
                    0x00, ResourceConsumer, ,)
                I2cSerialBus (0x000C, ControllerInitiated, 0x00061A80,
                    AddressingMode7Bit, "\\_SB.I2C4",
                    0x00, ResourceConsumer, ,)
                I2cSerialBus (0x0054, ControllerInitiated, 0x00061A80,
                    AddressingMode7Bit, "\\_SB.I2C4",
                    0x00, ResourceConsumer, ,)
            })
            Return (SBUF) /* \_SB_.I2C4.CAM1._CRS.SBUF */
        }
        ...

Furthermore those do not have names. At least the existing ones out
there, which is why I think we should instead refer them with integer
indexes. I think that works also with DT. Then provide an optional
"reg-names" or whatever that can be used to get secondary addresses with
certain name. For new stuff we can use names with ACPI _DSD method like:

    Name (_DSD, Package () {
        ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
        Package () {
            Package () {"reg-names", Package() {"primary", "secondary-1", "secondary-2"}}
        }
    })

Here "secondary-1" maps to second entry in _CRS. Although not sure how
useful the whole naming thing is.

> Signed-off-by: Jean-Michel Hautbois <jean-michel.hautbois@xxxxxxxxxxxx>
> ---
> v2: adding some DT bindings documentation (more than one year later...)
> 
>  Documentation/devicetree/bindings/i2c/i2c.txt |  7 +++++
>  drivers/i2c/i2c-core.c                        | 42 +++++++++++++++++++++++++++
>  include/linux/i2c.h                           |  5 ++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index c8d977e..f31b2ad 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -62,6 +62,13 @@ wants to support one of the below features, it should adapt the bindings below.
>  - wakeup-source
>  	device can be used as a wakeup source.
>  
> +- reg
> +	I2C slave addresses
> +
> +- reg-names
> +	Names of map programmable addresses.
> +	It can contain any map needing another address than default one.
> +
>  Binding may contain optional "interrupts" property, describing interrupts
>  used by the device. I2C core will assign "irq" interrupt (or the very first
>  interrupt if not using interrupt names) as primary interrupt for the slave.
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index ffe715d..da49fab 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -1158,6 +1158,48 @@ struct i2c_client *i2c_new_dummy(struct i2c_adapter *adapter, u16 address)
>  }
>  EXPORT_SYMBOL_GPL(i2c_new_dummy);
>  
> +/**
> + * i2c_new_secondary_device - Helper to get the instantiated secondary address
> + * and create the associated device
> + * @client: Handle to the primary client
> + * @name: Handle to specify which secondary address to get
> + * @default_addr: Used as a fallback if no secondary address was specified
> + * Context: can sleep
> + *
> + * I2C clients can be composed of multiple I2C slaves bound together in a single
> + * component. The I2C client driver then binds to the master I2C slave and needs
> + * to create I2C dummy clients to communicate with all the other slaves.
> + *
> + * This function creates and returns an I2C dummy client whose I2C address is
> + * retrieved from the platform firmware based on the given slave name. If no
> + * address is specified by the firmware default_addr is used.
> + *
> + * On DT-based platforms the address is retrieved from the "reg" property entry
> + * cell whose "reg-names" value matches the slave name.
> + *
> + * This returns the new i2c client, which should be saved for later use with
> + * i2c_unregister_device(); or NULL to indicate an error.
> + */
> +struct i2c_client *i2c_new_secondary_device(struct i2c_client *client,
> +						const char *name,
> +						u16 default_addr)
> +{
> +	struct device_node *np = client->dev.of_node;
> +	u32 addr = default_addr;
> +	int i;
> +
> +	if (np) {
> +		i = of_property_match_string(np, "reg-names", name);
> +		if (i >= 0)
> +			of_property_read_u32_index(np, "reg", i, &addr);
> +	}
> +
> +	dev_dbg(&client->adapter->dev, "Address for %s : 0x%x\n", name, addr);
> +	return i2c_new_dummy(client->adapter, addr);
> +}
> +EXPORT_SYMBOL_GPL(i2c_new_secondary_device);
> +
> +
>  /* ------------------------------------------------------------------------- */
>  
>  /* I2C bus adapters -- one roots each I2C or SMBUS segment */
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 200cf13b..9c90735 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -349,6 +349,11 @@ extern int i2c_probe_func_quick_read(struct i2c_adapter *, unsigned short addr);
>  extern struct i2c_client *
>  i2c_new_dummy(struct i2c_adapter *adap, u16 address);
>  
> +extern struct i2c_client *
> +i2c_new_secondary_device(struct i2c_client *client,
> +				const char *name,
> +				u16 default_addr);
> +
>  extern void i2c_unregister_device(struct i2c_client *);
>  #endif /* I2C */
>  
> -- 
> 2.7.0