linux-kernel - Re: [PATCH v3 2/3] x86/platform/p2sb: New Primary to Sideband bridge support driver for Intel SOC's

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Date:	Thu, 9 Jun 2016 17:05:38 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Tan Jui Nee <jui.nee.tan@...el.com>
Cc:	heikki.krogerus@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, ptyser@...-inc.com, lee.jones@...aro.org,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
	jonathan.yong@...el.com, ong.hock.yu@...el.com,
	weifeng.voon@...el.com, wan.ahmad.zainie.wan.mohamad@...el.com
Subject: Re: [PATCH v3 2/3] x86/platform/p2sb: New Primary to Sideband bridge
 support driver for Intel SOC's

On Tue, Jun 07, 2016 at 02:55:52PM +0800, Tan Jui Nee wrote:
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> 
> There is already one and at least one more user coming which
> require an access to Primary to Sideband bridge (P2SB) in order
> to get IO or MMIO bar hidden by BIOS.
> Create a driver to access P2SB for x86 devices.
> 
> Signed-off-by: Yong, Jonathan <jonathan.yong@...el.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  arch/x86/Kconfig                 | 14 ++++++
>  arch/x86/include/asm/p2sb.h      | 27 +++++++++++
>  arch/x86/platform/intel/Makefile |  1 +
>  arch/x86/platform/intel/p2sb.c   | 99 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 141 insertions(+)
>  create mode 100644 arch/x86/include/asm/p2sb.h
>  create mode 100644 arch/x86/platform/intel/p2sb.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 2dc18605..589045e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -606,6 +606,20 @@ config IOSF_MBI_DEBUG
>  
>  	  If you don't require the option or are in doubt, say N.
>  
> +config X86_INTEL_NON_ACPI
> +	bool "Enable support non-ACPI Intel platforms"
> +	select PINCTRL
> +	---help---
> +	  Select this option to enables MMIO BAR access over the P2SB for
> +	  non-ACPI Intel SoC platforms. This driver uses the P2SB hide/unhide
> +	  mechanism cooperatively to pass the PCI BAR address to the platform
> +	  driver, currently GPIO on the following SoC products.
> +	   - Apollo Lake

Why do we need Kconfig option for this?

I think better is to make P2SB available on CPUs which have one, and
that can be detected runtime. If P2SB is not available then p2sb_bar()
returns -ENODEV.