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Subject[tip:x86/dma] x86/i8237: Register device based on FADT legacy boot flag
Commit-ID:  f79b1c573cb4dc551919f81ed5797419f6fc1f3a
Gitweb: https://git.kernel.org/tip/f79b1c573cb4dc551919f81ed5797419f6fc1f3a
Author: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
AuthorDate: Thu, 29 Mar 2018 20:36:55 +0530
Committer: Thomas Gleixner <tglx@linutronix.de>
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® Core™ Processor
Platform Controller Hub Family: BIOS Specification.

Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: rjw@rjwysocki.net
Cc: hpa@zytor.com
Cc: Alan Cox <alan@linux.intel.com>
Link: https://lkml.kernel.org/r/1522336015-22994-1-git-send-email-anshuman.gupta@intel.com
---
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
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