Re: [RFC PATCH 0/4] Add ACPI support for pinctrl configuration

[Charles Garcia-Tobin]

On 04/04/2016 23:52, "Mark Rutland" <mark.rutland@xxxxxxx> wrote:

>Hi,
>
>On Thu, Mar 31, 2016 at 02:44:41PM +0300, Irina Tirdea wrote:
>> This is a proposal for adding ACPI support for pin controller
>> configuration.
>> 
>> It has been developed to enable the MinnowBoard and IoT community
>> by providing an easy way to specify pin multiplexing and
>> pin configuration.
>> 
>> This proposal is based on using _DSD properties to specify device
>> states and configuration nodes and it follows closely the device
>> tree model. Device states are defined using the Device Properties
>> format and the configuration nodes are defined using the
>> Hierarchical Properties Extension format. The generic properties
>> for the configuration nodes are the same as the ones for device
>> tree, while pincontroller drivers can also define custom ones.
>
>From a look of the Documentation addition, and of the current uses of
>pinctrl-names in device tree bindings, one reason for requiring multiple
>pinctrl states is power management. Given that, I'm somewhat concerned by
>this,
>as it goes against the usual ACPI model of abstracting this sort of thing
>behind power control methods.
>
>To the best of my knowledge, that goes against the ASWG's expectations on
>how
>_DSD will be used (per [1]). Charles, please correct me if that document
>is no
>longer representative.

It is though latest version was posted by Rafael a bit later:
https://lists.acpica.org/pipermail/dsd/2015-December/000027.html


In addition the core rules requiring that existing ACPI paradigms are not
subverted through DSD (basically the concern you express) are also
documented in the main DSD documentation itself:
http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UU
ID.pdf (section 2.3)


Cheers

Charles


>
>Additionally, pinctrl has some cross-cutting concerns (e.g. mutually
>exclusive
>device usage due to a shared pin), and I can imagine that may interact
>poorly
>with any AML or firmware assumptions about the state of the world, as
>there's
>no mechanism present to notify those of changes to pins.
>
>I think that this is a class of problem which needs to be raised with the
>ASWG,
>and solved in an ACPI-native fashion, rather than simply copying
>properties
>from DT using _DSD. If nothing else, the restrictions on FW and AML would
>need
>to be specified.
>
>Thanks,
>Mark.
>
>[1] https://lists.acpica.org/pipermail/dsd/2015-September/000019.html
>