Re: [PATCH v4] iio : Add cm3218 smbus ara and acpi support

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 20 Nov 2017 12:57:56 +0200
Mika Westerberg <mika.westerberg@linux.intel.com> wrote:

> +Jarkko
> 
> On Sun, Nov 19, 2017 at 04:35:51PM +0000, Jonathan Cameron wrote:
> > On Thu, 2 Nov 2017 16:04:07 +0100
> > Wolfram Sang <wsa@the-dreams.de> wrote:
> >   
> > > On Thu, Nov 02, 2017 at 02:35:50PM +0000, Jonathan Cameron wrote:  
> > > > On Fri, 27 Oct 2017 18:27:02 +0200
> > > > Marc CAPDEVILLE <m.capdeville@no-log.org> wrote:
> > > >     
> > > > > On asus T100, Capella cm3218 chip is implemented as ambiant light
> > > > > sensor. This chip expose an smbus ARA protocol device on standard
> > > > > address 0x0c. The chip is not functional before all alerts are
> > > > > acknowledged.
> > > > > On asus T100, this device is enumerated on ACPI bus and the
> > > > > description give tow I2C connection. The first is the connection to
> > > > > the ARA device and the second gives the real address of the device.
> > > > > 
> > > > > So, on device probe,If the i2c address is the ARA address and the
> > > > > device is enumerated via acpi, we lookup for the real address in
> > > > > the ACPI resource list and change it in the client structure.
> > > > > if an interrupt resource is given, and only for cm3218 chip,
> > > > > we declare an smbus_alert device.
> > > > > 
> > > > > Signed-off-by: Marc CAPDEVILLE <m.capdeville@no-log.org>    
> > > > 
> > > > Wolfram - this needs input from you on how to neatly handle
> > > > an ACPI registered ARA.    
> > > 
> > > ACPI is really not my field. Try asking the I2C ACPI maintainers or
> > > Benjamin Tissoires <benjamin.tissoires@redhat.com> who did work on SMBus
> > > interrupts recently.
> > >   
> > Hi Mika, Benjamin,
> > 
> > So we've lost most of the context in this thread, but the basic question
> > is how to handle smbus ARA support with ACPI. 
> > 
> > https://patchwork.kernel.org/patch/10030309/
> > 
> > Has the proposal made in this driver which is really not terribly nice
> > (as it registers the ARA device by messing with the address and registering
> > a second device).
> > 
> > As I understood it the ARA device registration should be handled by the
> > i2c master, but there are very few examples.
> > 
> > Phil pointed out that equivalent OF support recently got taken from him..
> > https://www.spinics.net/lists/devicetree/msg191947.html
> > https://www.spinics.net/lists/linux-i2c/msg31173.html
> > 
> > Any thoughts on the right way to do this?  
> 
> There does not seem to be any way in ACPI to tell which "connection" is
> used to describe ARA so that part currently is something each driver
> needs to handle as they know the device the best. I don't think we have
> any means to handle it in generic way in I2C core except to provide some
> helpers that work on top of i2c_setup_smbus_alert() but understand ACPI
> resources. Say provide function like this:
> 
>   int acpi_i2c_setup_smbus_alert(struct i2c_adapter *adapter, int index);
> 
> Which then extracts automatically I2cSerialBus connection from "index"
> and calls i2c_setup_smbus_alert() accordingly.
> 
> In the long run we could introduce _DSD property that can be used to
> name the connection in the same way DT does;
> 
>     Name (_CRS, ResourceTemplate () {
>         I2cSerialBus () { ... } // ARA
>         I2cSerialBus () { ... } // normal device address
>     })
> 
>     Name (_DSD, Package () {
>         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>         Package () {
>             Package () {"smbus_alert", 0} // Where 0 means the first I2cSerialBus
>             ...
>         }
>     })
> 
> But it does not help the existing systems.

I'm curious - how would we go about promoting this piece of common sense?

Jonathan


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