Re: [PATCH v3] x86: i8237: Register based on FADT legacy boot flag
From: Rajneesh Bhardwaj
Date: Thu Mar 22 2018 - 07:10:27 EST
On Thu, Mar 22, 2018 at 03:51:58PM +0530, Anshuman Gupta wrote:
Adding Thomas.
> From: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxxxx>
>
> 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 Coreâ 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@xxxxxxxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Signed-off-by: Anshuman Gupta <anshuman.gupta@xxxxxxxxx>
> Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxxxx>
> ---
> 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