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commit 777a7717d60ccdc9b84f35074f848d3f746fc3bf upstream. Ville noticed that the last mocs entry is used unconditionally by the HW when it performs cache evictions, and noted that while the value is not meant to be writable by the driver, we should program it to a reasonable value nevertheless. As it turns out, we can change the value of mocs:63 and the value we were programming into it would cause hard hangs in conjunction with atomic operations. v2: Add details from bspec about how it is used by HW Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2707 Fixes: 3bbaba0ceaa2 ("drm/i915: Added Programming of the MOCS") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Jason Ekstrand <jason@jlekstrand.net> Cc: <stable@vger.kernel.org> # v4.3+ Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20201126140841.1982-1-chris@chris-wilson.co.uk (cherry picked from commit 977933b5da7c16f39295c4c1d4259a58ece65dbe) Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>