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

[Sudeep Holla <sudeep.holla@arm.com>]

On 02/03/15 11:29, Suzuki K. Poulose wrote:
> From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>
>
> 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.
>
> Cc: devicetree@vger.kernel.org
> Cc: Punit Agrawal <punit.agrawal@arm.com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
> ---
>   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/arch/arm/include/asm/arm-cci.h b/arch/arm/include/asm/arm-cci.h
> new file mode 100644
> index 0000000..936e74a
> --- /dev/null
> +++ b/arch/arm/include/asm/arm-cci.h
> @@ -0,0 +1,42 @@
> +/*
> + * arch/arm/include/asm/arm-cci.h
> + *
> + * Copyright (C) 2015 ARM Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef __ASM_ARM_CCI_H
> +#define __ASM_ARM_CCI_H
> +
> +#ifdef CONFIG_MCPM
> +#include <asm/mcpm.h>
> +
> +/*
> + * We don't have a reliable way of detecting whether,
> + * if we have access to secure-only registers, unless
> + * mcpm is registered.
> + */
> +static inline int platform_has_secure_cci_access(void)

bool instead of int might be more apt here ?

Regards,
Sudeep