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We can implement limited RC6 counter wrap-around protection under the assumption that clients will be reading this value more frequently than the wrap period on a given platform. With the typical wrap-around period being ~90 minutes, even with the exception of Baytrail which wraps every 13 seconds, this sounds like a reasonable assumption. Implementation works by storing a 64-bit software copy of a hardware RC6 counter, along with the previous HW counter snapshot. This enables it to detect wrap is polled frequently enough and keep the software copy monotonically incrementing. v2: * Missed GEN6_GT_GFX_RC6_LOCKED when considering slot sizing and indexing. * Fixed off-by-one in wrap-around handling. (Chris Wilson) v3: * Simplify index checking by using unsigned int. (Chris Wilson) * Expand the comment to explain why indexing works. v4: * Use __int128 if supported. v5: * Use mul_u64_u32_div. (Chris Wilson) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94852 Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> # v3 Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Link: https://patchwork.freedesktop.org/patch/msgid/20180208160036.29919-1-tvrtko.ursulin@linux.intel.com Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.