Commits
Rajneesh Bhardwaj committed f79b1c573cb
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