From 928f8f42310f244501a7c70daac82c196112c190 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 19 Apr 2019 12:17:47 +0100 Subject: [PATCH] drm/i915/ringbuffer: EMIT_INVALIDATE *before* switch context MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Despite what I think the prm recommends, commit f2253bd9859b ("drm/i915/ringbuffer: EMIT_INVALIDATE after switch context") turned out to be a huge mistake when enabling Ironlake contexts as the GPU would hang on either a MI_FLUSH or PIPE_CONTROL immediately following the MI_SET_CONTEXT of an active mesa context (more vanilla contexts, e.g. simple rendercopies with igt, do not suffer). Ville found the following clue, "[DevCTG+]: For the invalidate operation of the pipe control, the following pointers are affected. The invalidate operation affects the restore of these packets. If the pipe control invalidate operation is completed before the context save, the indirect pointers will not be restored from memory. 1. Pipeline State Pointer 2. Media State Pointer 3. Constant Buffer Packet" which suggests by us emitting the INVALIDATE prior to the MI_SET_CONTEXT, we prevent the context-restore from chasing the dangling pointers within the image, and explains why this likely prevents the GPU hang. Signed-off-by: Chris Wilson Reviewed-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20190419111749.3910-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/gt/intel_ringbuffer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c b/drivers/gpu/drm/i915/gt/intel_ringbuffer.c index b791da2711e0..1418ed0c4875 100644 --- a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/gt/intel_ringbuffer.c @@ -1886,12 +1886,12 @@ static int ring_request_alloc(struct i915_request *request) */ request->reserved_space += LEGACY_REQUEST_SIZE; - ret = switch_context(request); + /* Unconditionally invalidate GPU caches and TLBs. */ + ret = request->engine->emit_flush(request, EMIT_INVALIDATE); if (ret) return ret; - /* Unconditionally invalidate GPU caches and TLBs. */ - ret = request->engine->emit_flush(request, EMIT_INVALIDATE); + ret = switch_context(request); if (ret) return ret;