[PATCH v4] x86: i8237: Register based on FADT legacy boot flag

[Anshuman Gupta]

From: Rajneesh Bhardwaj 

>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.
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 
Reviewed-by: Andy Shevchenko 
Signed-off-by: Anshuman Gupta 
Signed-off-by: Rajneesh Bhardwaj 
---
Changes in v4:
 * Modified the commit message about cut-off date year 2017.

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 
 #include 
 #include 
 
 #include 
+#include 
 
 /*
  * 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(_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

[PATCH v4] x86: i8237: Register based on FADT legacy boot flag

[Anshuman Gupta]

From: Rajneesh Bhardwaj 

>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.
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 
Reviewed-by: Andy Shevchenko 
Signed-off-by: Anshuman Gupta 
Signed-off-by: Rajneesh Bhardwaj 
---
Changes in v4:
 * Modified the commit message about cut-off date year 2017.

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 
 #include 
 #include 
 
 #include 
+#include 
 
 /*
  * 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(_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