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Date:   Thu, 22 Mar 2018 16:35:15 +0530
From:   Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
To:     Anshuman Gupta <anshuman.gupta@intel.com>
Cc:     tglx@linutronix.de, x86@kernel.org, mingo@redhat.com,
        hpa@zytor.com, rjw@rjwysocki.net,
        andriy.shevchenko@linux.intel.com, alan@linux.intel.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] x86: i8237: Register based on FADT legacy boot flag
Message-ID: <20180322110515.GA3849@raj-desk2.iind.intel.com>
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On Thu, Mar 22, 2018 at 03:51:58PM +0530, Anshuman Gupta wrote:

Adding Thomas.

> From: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
> 
> From Skylake onwards, the platform controller hub (Sunrisepoint PCH) does
> not support legacy DMA operations to IO ports 81h-83h, 87h, 89h-8Bh, 8Fh.
> Currently this driver registers as syscore ops and its resume function is
> called on every resume from S3. On Skylake and Kabylake, this causes a
> resume delay of around 100ms due to port IO operations, which is a problem.
> 
> This change allows to load the driver only when the platform bios
> explicitly supports such devices or has a cut-off date earlier than 2017.
> For example open source system firmware like coreboot started unsetting
> ACPI_FADT_LEGACY_DEVICES field in FADT table very recently.
> https://github.com/coreboot/coreboot/blob/05132707ca1e13a11cd13c77326bc65011b09feb/src/soc/intel/skylake/acpi.c#L271
> 
> Please refer to chapter 21 of 6th Generation Intel® Core™ Processor
> Platform Controller Hub Family: BIOS Specification.
> 
> https://www.intel.in/content/www/in/en/embedded/products/skylake/u-mobile/software-and-drivers.html
> 
> Cc: Alan Cox <alan@linux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
> Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
> ---
> Changes in v3:
>  * Added x86_pnpbios_disabled and using it instead of pnpbios.
>  * Modified the commit message.
> 
> Changes in v2:
>  * changed to dma_inb()
> ---
>  arch/x86/include/asm/x86_init.h   |  1 +
>  arch/x86/kernel/i8237.c           | 25 +++++++++++++++++++++++++
>  arch/x86/kernel/platform-quirks.c |  7 ++++++-
>  3 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index fc2f082..b6ceac0 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -286,6 +286,7 @@ extern struct x86_msi_ops x86_msi;
>  extern struct x86_io_apic_ops x86_io_apic_ops;
>  
>  extern void x86_early_init_platform_quirks(void);
> +extern bool x86_pnpbios_disabled(void);
>  extern void x86_init_noop(void);
>  extern void x86_init_uint_noop(unsigned int unused);
>  
> diff --git a/arch/x86/kernel/i8237.c b/arch/x86/kernel/i8237.c
> index 8eeaa81..0a3e70f 100644
> --- a/arch/x86/kernel/i8237.c
> +++ b/arch/x86/kernel/i8237.c
> @@ -9,10 +9,12 @@
>   * your option) any later version.
>   */
>  
> +#include <linux/dmi.h>
>  #include <linux/init.h>
>  #include <linux/syscore_ops.h>
>  
>  #include <asm/dma.h>
> +#include <asm/x86_init.h>
>  
>  /*
>   * This module just handles suspend/resume issues with the
> @@ -49,6 +51,29 @@ static struct syscore_ops i8237_syscore_ops = {
>  
>  static int __init i8237A_init_ops(void)
>  {
> +	/*
> +	 * From SKL PCH onwards, the legacy DMA device is removed in which the
> +	 * I/O ports (81h-83h, 87h, 89h-8Bh, 8Fh) related to it are removed
> +	 * as well. All removed ports must return 0xff for a inb() request.
> +	 *
> +	 * Note: DMA_PAGE_2 (port 0x81) should not be checked for detecting
> +	 * the presence of DMA device since it may be used by BIOS to decode
> +	 * LPC traffic for POST codes. Original LPC only decodes one byte of
> +	 * port 0x80 but some BIOS may choose to enhance PCH LPC port 0x8x
> +	 * decoding.
> +	 */
> +	if (dma_inb(DMA_PAGE_0) == 0xFF)
> +		return -ENODEV;
> +
> +	/*
> +	 * It is not required to load this driver as newer SoC may not
> +	 * support 8237 DMA or bus mastering from LPC. Platform firmware
> +	 * must announce the support for such legacy devices via
> +	 * ACPI_FADT_LEGACY_DEVICES field in FADT table.
> +	 */
> +	if (x86_pnpbios_disabled() && dmi_get_bios_year() >= 2017)
> +		return -ENODEV;
> +
>  	register_syscore_ops(&i8237_syscore_ops);
>  	return 0;
>  }
> diff --git a/arch/x86/kernel/platform-quirks.c b/arch/x86/kernel/platform-quirks.c
> index 235fe60..b348a67 100644
> --- a/arch/x86/kernel/platform-quirks.c
> +++ b/arch/x86/kernel/platform-quirks.c
> @@ -33,9 +33,14 @@ void __init x86_early_init_platform_quirks(void)
>  		x86_platform.set_legacy_features();
>  }
>  
> +bool __init x86_pnpbios_disabled(void)
> +{
> +	return x86_platform.legacy.devices.pnpbios == 0;
> +}
> +
>  #if defined(CONFIG_PNPBIOS)
>  bool __init arch_pnpbios_disabled(void)
>  {
> -	return x86_platform.legacy.devices.pnpbios == 0;
> +	return x86_pnpbios_disabled();
>  }
>  #endif
> -- 
> 2.7.4
> 

-- 
Best Regards,
Rajneesh