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

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Date:	Thu, 14 Apr 2016 21:10:33 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Jean-Michel Hautbois <jhautbois@...il.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	devicetree@...r.kernel.org, galak@...eaurora.org,
	ijc+devicetree@...lion.org.uk, mark.rutland@....com,
	pawel.moll@....com, robh+dt@...nel.org,
	laurent.pinchart@...asonboard.com, lars@...afoo.de,
	Jean-Michel Hautbois <jean-michel.hautbois@...-labs.com>
Subject: Re: [PATCH v2] i2c: Add generic support passing secondary devices
 addresses

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.

With "no default address" you mean the function parameter is 0? Yeah,
you get a NULL pointer from i2c_new_device then, but also a dev_err
message, or?

> 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.

Ccing Mika. I think it can be 1:1 converted to device_property_*
functions already giving ACPI support for free?

Thanks,

   Wolfram


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