From 1fc719d13ac07b082ff9daa8f40254680cade111 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Mon, 11 Jun 2018 11:48:08 +0100 Subject: [PATCH] drm/i915/ringbuffer: Brute force context restore An issue encountered with switching mm on gen7 is that the GPU likes to hang (with the VS unit busy) when told to force restore the current context. We can simply workaround this by substituting the MI_FORCE_RESTORE flag with a round-trip through the kernel_context, forcing the context to be saved and restored; thereby reloading the PP_DIR registers and updating the modified page directory! v2: Undo attempted optimisation in caller (Tvrtko) Signed-off-by: Chris Wilson Cc: Joonas Lahtinen Cc: Mika Kuoppala Cc: Matthew Auld Cc: Tvrtko Ursulin Reviewed-by: Joonas Lahtinen Reviewed-by: Mika Kuoppala Link: https://patchwork.freedesktop.org/patch/msgid/20180611104808.24295-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/intel_ringbuffer.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index 6496c1d00dbb..5bc53a5f4504 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -1456,6 +1456,7 @@ static inline int mi_set_context(struct i915_request *rq, u32 flags) (HAS_LEGACY_SEMAPHORES(i915) && IS_GEN7(i915)) ? INTEL_INFO(i915)->num_rings - 1 : 0; + bool force_restore = false; int len; u32 *cs; @@ -1469,6 +1470,12 @@ static inline int mi_set_context(struct i915_request *rq, u32 flags) len = 4; if (IS_GEN7(i915)) len += 2 + (num_rings ? 4*num_rings + 6 : 0); + if (flags & MI_FORCE_RESTORE) { + GEM_BUG_ON(flags & MI_RESTORE_INHIBIT); + flags &= ~MI_FORCE_RESTORE; + force_restore = true; + len += 2; + } cs = intel_ring_begin(rq, len); if (IS_ERR(cs)) @@ -1493,6 +1500,26 @@ static inline int mi_set_context(struct i915_request *rq, u32 flags) } } + if (force_restore) { + /* + * The HW doesn't handle being told to restore the current + * context very well. Quite often it likes goes to go off and + * sulk, especially when it is meant to be reloading PP_DIR. + * A very simple fix to force the reload is to simply switch + * away from the current context and back again. + * + * Note that the kernel_context will contain random state + * following the INHIBIT_RESTORE. We accept this since we + * never use the kernel_context state; it is merely a + * placeholder we use to flush other contexts. + */ + *cs++ = MI_SET_CONTEXT; + *cs++ = i915_ggtt_offset(to_intel_context(i915->kernel_context, + engine)->state) | + MI_MM_SPACE_GTT | + MI_RESTORE_INHIBIT; + } + *cs++ = MI_NOOP; *cs++ = MI_SET_CONTEXT; *cs++ = i915_ggtt_offset(rq->hw_context->state) | flags; -- 2.11.0