linux-kernel - Re: [UPDATED] [PATCH 3/5] arm-cci: Get rid of secure transactions for PMU driver

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Date:	Thu, 19 Mar 2015 17:25:31 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	"Suzuki K. Poulose" <suzuki.poulose@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Nicolas Pitre <nico@...aro.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	Arnd Bergmann <arnd@...db.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Olof Johansson <olof@...om.net>,
	Pawel Moll <Pawel.Moll@....com>,
	Punit Agrawal <Punit.Agrawal@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [UPDATED] [PATCH 3/5] arm-cci: Get rid of secure transactions
 for PMU driver

On Tue, Mar 17, 2015 at 09:51:41AM +0000, Suzuki K. Poulose wrote:
> From: "Suzuki K. Poulose" <suzuki.poulose@....com>
> 
> A minor change, fixed missplled 'DEPRECATED' in the dev_warn().
> 
> Thanks
> Suzuki
> 
> ----8>----
> Avoid secure transactions while probing the CCI PMU. The
> existing code makes use of the Peripheral ID2 (PID2) register
> to determine the revision of the CCI400, which requires a
> secure transaction. This puts a limitation on the usage of the
> driver on systems running non-secure Linux(e.g, ARM64).
> 
> Updated the device-tree binding for cci pmu node to add the explicit
> revision number for the compatible field.
> 
> The supported strings are :
> 	arm,cci-400-pmu,r0
> 	arm,cci-400-pmu,r1
> 	arm,cci-400-pmu - DEPRECATED. See NOTE below
> 
> NOTE: If the revision is not mentioned, we need to probe the cci revision,
> which could be fatal on a platform running non-secure. We need a reliable way
> to know if we can poke the CCI registers at runtime on ARM32. We depend on
> 'mcpm_is_available()' when it is available. mcpm_is_available() returns true
> only when there is a registered driver for mcpm. Otherwise, we assume that we
> don't have secure access, and skips probing the revision number(ARM64 case).
> 
> The MCPM should figure out if it is safe to access the CCI. Unfortunately
> there isn't a reliable way to indicate the same via dtb. This patch doesn't
> address/change the current situation. It only deals with the CCI-PMU, leaving
> the assumptions about the secure access as it has been, prior to this patch.
> 
> Changes since V2:
>  - Use 'bool' instead of 'int' for platform_has_secure_cci_access().
>    (Suggested-by: Sudeep Holla)
> 
> Cc: devicetree@...r.kernel.org
> Cc: Punit Agrawal <punit.agrawal@....com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
> Tested-by: Sudeep Holla <sudeep.holla@....com>
> Acked-by: Nicolas Pitre <nicolas.pitre@...aro.org>
> ---
>  Documentation/devicetree/bindings/arm/cci.txt |    7 +++--
>  arch/arm/include/asm/arm-cci.h                |   42 +++++++++++++++++++++++++
>  arch/arm64/include/asm/arm-cci.h              |   27 ++++++++++++++++
>  drivers/bus/arm-cci.c                         |   17 +++++++++-
>  include/linux/arm-cci.h                       |    2 ++
>  5 files changed, 92 insertions(+), 3 deletions(-)
>  create mode 100644 arch/arm/include/asm/arm-cci.h
>  create mode 100644 arch/arm64/include/asm/arm-cci.h
> 
> diff --git a/Documentation/devicetree/bindings/arm/cci.txt b/Documentation/devicetree/bindings/arm/cci.txt
> index f28d82b..0e4b6a7 100644
> --- a/Documentation/devicetree/bindings/arm/cci.txt
> +++ b/Documentation/devicetree/bindings/arm/cci.txt
> @@ -94,8 +94,11 @@ specific to ARM.
>  		- compatible
>  			Usage: required
>  			Value type: <string>
> -			Definition: must be "arm,cci-400-pmu"
> -
> +			Definition: Supported strings are :

I'd prefer we said "Must contain one of:".

> +				 "arm,cci-400-pmu,r0"
> +				 "arm,cci-400-pmu,r1"
> +				 "arm,cci-400-pmu"  - DEPRECATED, permitted only where OS has
> +						      secure acces to CCI registers

Otherwise, the binding change looks fine to me, so:

Acked-by: Mark Rutland <mark.rutland@....com> [DT binding]
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