Subject: [PATCH v2 5/5] drivers: firmware: psci: add PSCI v1.0 DT bindings

From: [email-masked] (Andre Przywara)
Date: Mon, 5 Oct 2015 12:48:09 +0100

Hi Lorenzo,

sorry for this late reply, but this came up recently during an IRC
discussion:

On 08/07/15 18:16, Lorenzo Pieralisi wrote:
> PSCI 1.0 is designed to be fully compliant to the PSCI 0.2
> specification, with minor differences that are described in the
> PSCI specification.

So if PSCI 1.0 is fully compliant to the 0.2 spec and PSCI 0.2 mandates
a version function, why do we need a new binding here?
IIRC device tree bindings are just for features that cannot be probed,
whereas the availability of PSCI 1.0 features can be safely probed by
issuing the PSCI_VERSION call and checking for bits [16:32] >= 1.
So can't we just skip this extra binding and keep the compatible string
to 0.2 for every upcoming PSCI implementation?
This should actually be the last binding we need, since availability of
specific functions can be checked as well with the PSCI_FEATURES call in
the future.

Cheers,
Andre

> 
> In particular, PSCI v1.0 augments the specification with a new
> power_state format (extended stateid - probeable through the
> PSCI_FEATURES call), changes some function return codes and
> functions usage requirements wrt PSCI 0.2. These changes mean
> that 1.0 vs 0.2 compliancy should be enforced through a DT
> compatible string that allows firmware to specify 1.0 only
> compliancy so that older kernels are prevented from using
> PSCI 1.0 FW implementations in a non-compatible way (eg by
> calling a 1.0 FW implementation and expecting 0.2 behaviour).
> 
> This patch adds PSCI 1.0 DT bindings and related compatible
> string.
> 
> Signed-off-by: Lorenzo Pieralisi <[email-masked]>
> Acked-by: Sudeep Holla <[email-masked]>
> Cc: Mark Rutland <[email-masked]>
> ---
>  Documentation/devicetree/bindings/arm/psci.txt | 6 ++++++
>  drivers/firmware/psci.c                        | 1 +
>  2 files changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt
> index 5aa40ed..a9adab8 100644
> --- a/Documentation/devicetree/bindings/arm/psci.txt
> +++ b/Documentation/devicetree/bindings/arm/psci.txt
> @@ -31,6 +31,10 @@ Main node required properties:
>  					support, but are permitted to be present for compatibility with
>  					existing software when "arm,psci" is later in the compatible list.
>  
> +				* "arm,psci-1.0" : for implementations complying to PSCI 1.0. PSCI 1.0 is
> +					backward compatible with PSCI 0.2 with minor specification updates,
> +					as defined in the PSCI specification[2].
> +
>   - method        : The method of calling the PSCI firmware. Permitted
>                     values are:
>  
> @@ -100,3 +104,5 @@ Case 3: PSCI v0.2 and PSCI v0.1.
>  
>  [1] Kernel documentation - ARM idle states bindings
>      Documentation/devicetree/bindings/arm/idle-states.txt
> +[2] Power State Coordination Interface (PSCI) specification
> +    http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
> diff --git a/drivers/firmware/psci.c b/drivers/firmware/psci.c
> index bd2ba5b..5b544d7 100644
> --- a/drivers/firmware/psci.c
> +++ b/drivers/firmware/psci.c
> @@ -392,6 +392,7 @@ out_put_node:
>  static const struct of_device_id psci_of_match[] __initconst = {
>  	{ .compatible = "arm,psci",	.data = psci_0_1_init},
>  	{ .compatible = "arm,psci-0.2",	.data = psci_0_2_init},
> +	{ .compatible = "arm,psci-1.0",	.data = psci_0_2_init},
>  	{},
>  };
>  
>