[tip:x86/dma] x86/i8237: Register device based on FADT legacy boot flag

[tip-bot for Rajneesh Bhardwaj]

Commit-ID:  f79b1c573cb4dc551919f81ed5797419f6fc1f3a
Gitweb:     https://git.kernel.org/tip/f79b1c573cb4dc551919f81ed5797419f6fc1f3a
Author:     Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxxxx>
AuthorDate: Thu, 29 Mar 2018 20:36:55 +0530
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 27 Apr 2018 16:44:29 +0200

x86/i8237: Register device based on FADT legacy boot flag

>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
due to the following reasons:

   - The platforms released before year 2017 have support for the 8237.
     (except Sunrisepoint PCH e.g. Skylake)

   - Some of the BIOS that were released for platforms (Skylake, Kabylake)
     during 2016-17 are buggy. These BIOS do not set/unset the
     ACPI_FADT_LEGACY_DEVICES field in FADT table properly based on the
     presence or absence of the DMA device.

Very recently, open source system firmware like coreboot started unsetting
ACPI_FADT_LEGACY_DEVICES field in FADT table if the 8237 DMA device is not
present on the PCH.

Please refer to chapter 21 of 6th Generation Intel Coreâ Processor
Platform Controller Hub Family: BIOS Specification.

Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxxxx>
Signed-off-by: Anshuman Gupta <anshuman.gupta@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: rjw@xxxxxxxxxxxxx
Cc: hpa@xxxxxxxxx
Cc: Alan Cox <alan@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/1522336015-22994-1-git-send-email-anshuman.gupta@xxxxxxxxx
---
 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 ce8b4da07e35..db98e3ab3295 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -301,5 +301,6 @@ extern struct x86_apic_ops x86_apic_ops;
 extern void x86_early_init_platform_quirks(void);
 extern void x86_init_noop(void);
 extern void x86_init_uint_noop(unsigned int unused);
+extern bool x86_pnpbios_disabled(void);
 
 #endif
diff --git a/arch/x86/kernel/i8237.c b/arch/x86/kernel/i8237.c
index 8eeaa81de066..0a3e70fd00d6 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 235fe6008ac8..b348a672f71d 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