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There are two issues with the current RPCS programming for Icelake: Expansion of the slice count bitfield has been missed, as well as the required programming workaround for the subslice count bitfield size limitation. 1) Bitfield width for configuring the active slice count has grown so we need to program the GEN8_R_PWR_CLK_STATE accordingly. Current code was always requesting eight times the number of slices (due writing to a bitfield starting three bits higher than it should). These requests were luckily a) capped by the hardware to the available number of slices, and b) we haven't yet exported the code to ask for reduced slice configurations. Due both of the above there was no impact from this incorrect programming but we should still fix it. 2) Due subslice count bitfield being only three bits wide and furthermore capped to a maximum documented value of four, special programming workaround is needed to enable more than four subslices. With this programming driver has to consider the GT configuration as 2x4x8, while the hardware internally translates this to 1x8x8. A limitation stemming from this is that either a subslice count between one and four can be selected, or a subslice count equaling the total number of subslices in all selected slices. In other words, odd subslice counts greater than four are impossible, as are odd subslice counts greater than a single slice subslice count. This also had no impact in the current code base due breakage from 1) always reqesting more than one slice. While fixing this we also add some asserts to flag up any future bitfield overflows. v2: * Use a local in all branches for clarity. (Lionel) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bspec: 12247 Reported-by: tony.ye@intel.com Suggested-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com> Cc: tony.ye@intel.com Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180903113007.2643-1-tvrtko.ursulin@linux.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.
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.