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07431945d8
Intel hardware officially only supports GTTMMADR register accesses of 32-bits or less (although 64-bit accesses to device memory and PTEs in the GSM are fine). Even though we do usually seem to get back reasonable values when performing readq() operations on registers in BAR0, we shouldn't rely on this violation of the spec working consistently. It's likely that even when we do get proper register values back the hardware is internally satisfying the request via a non-atomic sequence of two 32-bit reads, which can be problematic for timestamps and counters if rollover of the lower bits is not considered. Replace xe_mmio_read64() with xe_mmio_read64_2x32() that implements 64-bit register reads as two 32-bit reads and attempts to ensure that the upper dword has stabilized to avoid problematic rollovers for counter and timestamp registers. v2: - Move function from xe_mmio.h to xe_mmio.c. (Lucas) - Convert comment to kerneldoc and note that it shouldn't be used on registers where reads may trigger side effects. (Lucas) Bspec: 60027 Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com> Reviewed-by: José Roberto de Souza <jose.souza@intel.com> Link: https://lore.kernel.org/r/20230823003312.1356779-3-matthew.d.roper@intel.com Signed-off-by: Matt Roper <matthew.d.roper@intel.com> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.