On Tue, Apr 12, 2016 at 09:03:08PM +0100, Chris Wilson wrote:
> After mi_set_context() succeeds, we need to update the state of the
> engine's last_context. This ensures that we hold a pin on the context
> whilst the hardware may write to it. However, since we didn't complete
> the post-switch setup of the context, we need to force the subsequent
> use of the same context to complete the setup (which means updating
> should_skip_switch()).
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
> Cc: Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com>
Specializing do_rcs_switch makes sense, but shouldn't be intermingled with
the bugfix. Assuming I'm reading things correctly the real bugfix is to
add the check for hw_ctx.initialized to should_skip_switch()? If so,
please split into 2 patches - first to add just that check, 2nd to do the
RCS specialization.
-Daniel
> ---
> drivers/gpu/drm/i915/i915_gem_context.c | 215
> ++++++++++++++++----------------
> 1 file changed, 109 insertions(+), 106 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c
> b/drivers/gpu/drm/i915/i915_gem_context.c
> index e5ad7b21e356..361959b1d53a 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -609,50 +609,40 @@ mi_set_context(struct drm_i915_gem_request *req, u32
> hw_flags)
> return ret;
> }
>
> -static inline bool should_skip_switch(struct intel_engine_cs *engine,
> - struct intel_context *from,
> +static inline bool should_skip_switch(struct intel_context *from,
> struct intel_context *to)
> {
> if (to->remap_slice)
> return false;
>
> - if (to->ppgtt && from == to &&
> - !(intel_engine_flag(engine) & to->ppgtt->pd_dirty_rings))
> - return true;
> + if (!to->legacy_hw_ctx.initialized)
> + return false;
>
> - return false;
> + if (to->ppgtt && to->ppgtt->pd_dirty_rings & (1 << RCS))
> + return false;
> +
> + return to == from;
> }
>
> static bool
> -needs_pd_load_pre(struct intel_engine_cs *engine, struct intel_context *to)
> +needs_pd_load_pre(struct intel_context *to)
> {
> - struct drm_i915_private *dev_priv = engine->dev->dev_private;
> -
> if (!to->ppgtt)
> return false;
>
> - if (INTEL_INFO(engine->dev)->gen < 8)
> - return true;
> -
> - if (engine != &dev_priv->engine[RCS])
> + if (INTEL_INFO(to->i915)->gen < 8)
> return true;
>
> return false;
> }
>
> static bool
> -needs_pd_load_post(struct intel_engine_cs *engine, struct intel_context *to,
> - u32 hw_flags)
> +needs_pd_load_post(struct intel_context *to, u32 hw_flags)
> {
> - struct drm_i915_private *dev_priv = engine->dev->dev_private;
> -
> if (!to->ppgtt)
> return false;
>
> - if (!IS_GEN8(engine->dev))
> - return false;
> -
> - if (engine != &dev_priv->engine[RCS])
> + if (!IS_GEN8(to->i915))
> return false;
>
> if (hw_flags & MI_RESTORE_INHIBIT)
> @@ -661,60 +651,33 @@ needs_pd_load_post(struct intel_engine_cs *engine,
> struct intel_context *to,
> return false;
> }
>
> -static int do_switch(struct drm_i915_gem_request *req)
> +static int do_rcs_switch(struct drm_i915_gem_request *req)
> {
> struct intel_context *to = req->ctx;
> struct intel_engine_cs *engine = req->engine;
> - struct drm_i915_private *dev_priv = req->i915;
> - struct intel_context *from = engine->last_context;
> - u32 hw_flags = 0;
> - bool uninitialized = false;
> + struct intel_context *from;
> + u32 hw_flags;
> int ret, i;
>
> - if (from != NULL && engine == &dev_priv->engine[RCS]) {
> - BUG_ON(from->legacy_hw_ctx.rcs_state == NULL);
> - BUG_ON(!i915_gem_obj_is_pinned(from->legacy_hw_ctx.rcs_state));
> - }
> -
> - if (should_skip_switch(engine, from, to))
> + if (should_skip_switch(engine->last_context, to))
> return 0;
>
> /* Trying to pin first makes error handling easier. */
> - if (engine == &dev_priv->engine[RCS]) {
> - ret = i915_gem_obj_ggtt_pin(to->legacy_hw_ctx.rcs_state,
> - get_context_alignment(engine->dev),
> - 0);
> - if (ret)
> - return ret;
> - }
> + ret = i915_gem_obj_ggtt_pin(to->legacy_hw_ctx.rcs_state,
> + get_context_alignment(engine->dev),
> + 0);
> + if (ret)
> + return ret;
>
> /*
> * Pin can switch back to the default context if we end up calling into
> * evict_everything - as a last ditch gtt defrag effort that also
> * switches to the default context. Hence we need to reload from here.
> + *
> + * XXX: Doing so is painfully broken!
> */
> from = engine->last_context;
>
> - if (needs_pd_load_pre(engine, to)) {
> - /* Older GENs and non render rings still want the load first,
> - * "PP_DCLV followed by PP_DIR_BASE register through Load
> - * Register Immediate commands in Ring Buffer before submitting
> - * a context."*/
> - trace_switch_mm(engine, to);
> - ret = to->ppgtt->switch_mm(to->ppgtt, req);
> - if (ret)
> - goto unpin_out;
> -
> - /* Doing a PD load always reloads the page dirs */
> - to->ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
> - }
> -
> - if (engine != &dev_priv->engine[RCS]) {
> - if (from)
> - i915_gem_context_unreference(from);
> - goto done;
> - }
> -
> /*
> * Clear this page out of any CPU caches for coherent swap-in/out. Note
> * that thanks to write = false in this call and us not setting any gpu
> @@ -727,55 +690,46 @@ static int do_switch(struct drm_i915_gem_request *req)
> if (ret)
> goto unpin_out;
>
> - if (!to->legacy_hw_ctx.initialized || i915_gem_context_is_default(to)) {
> - hw_flags |= MI_RESTORE_INHIBIT;
> + if (needs_pd_load_pre(to)) {
> + /* Older GENs and non render rings still want the load first,
> + * "PP_DCLV followed by PP_DIR_BASE register through Load
> + * Register Immediate commands in Ring Buffer before submitting
> + * a context."*/
> + trace_switch_mm(engine, to);
> + ret = to->ppgtt->switch_mm(to->ppgtt, req);
> + if (ret)
> + goto unpin_out;
> +
> + /* Doing a PD load always reloads the page dirs */
> + to->ppgtt->pd_dirty_rings &= ~(1 << RCS);
> + }
> +
> + if (!to->legacy_hw_ctx.initialized || i915_gem_context_is_default(to))
> /* NB: If we inhibit the restore, the context is not allowed to
> * die because future work may end up depending on valid address
> * space. This means we must enforce that a page table load
> * occur when this occurs. */
> - } else if (to->ppgtt &&
> - (intel_engine_flag(engine) & to->ppgtt->pd_dirty_rings)) {
> - hw_flags |= MI_FORCE_RESTORE;
> - to->ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
> - }
> + hw_flags = MI_RESTORE_INHIBIT;
> + else if (to->ppgtt && to->ppgtt->pd_dirty_rings & (1 << RCS))
> + hw_flags = MI_FORCE_RESTORE;
> + else
> + hw_flags = 0;
>
> /* We should never emit switch_mm more than once */
> - WARN_ON(needs_pd_load_pre(engine, to) &&
> - needs_pd_load_post(engine, to, hw_flags));
> + WARN_ON(needs_pd_load_pre(to) && needs_pd_load_post(to, hw_flags));
>
> - ret = mi_set_context(req, hw_flags);
> - if (ret)
> - goto unpin_out;
> -
> - /* GEN8 does *not* require an explicit reload if the PDPs have been
> - * setup, and we do not wish to move them.
> - */
> - if (needs_pd_load_post(engine, to, hw_flags)) {
> - trace_switch_mm(engine, to);
> - ret = to->ppgtt->switch_mm(to->ppgtt, req);
> - /* The hardware context switch is emitted, but we haven't
> - * actually changed the state - so it's probably safe to bail
> - * here. Still, let the user know something dangerous has
> - * happened.
> - */
> + if (to != from || (hw_flags & MI_FORCE_RESTORE)) {
> + ret = mi_set_context(req, hw_flags);
> if (ret) {
> - DRM_ERROR("Failed to change address space on context
> switch\n");
> + /* Force the reload of this and the previous mm */
> + if (needs_pd_load_pre(to))
> + to->ppgtt->pd_dirty_rings |= 1 << RCS;
> + if (from && needs_pd_load_pre(from))
> + from->ppgtt->pd_dirty_rings |= 1 << RCS;
> goto unpin_out;
> }
> }
>
> - for (i = 0; i < MAX_L3_SLICES; i++) {
> - if (!(to->remap_slice & (1<<i)))
> - continue;
> -
> - ret = i915_gem_l3_remap(req, i);
> - /* If it failed, try again next round */
> - if (ret)
> - DRM_DEBUG_DRIVER("L3 remapping failed\n");
> - else
> - to->remap_slice &= ~(1<<i);
> - }
> -
> /* The backing object for the context is done after switching to the
> * *next* context. Therefore we cannot retire the previous context until
> * the next context has already started running. In fact, the below code
> @@ -798,27 +752,52 @@ static int do_switch(struct drm_i915_gem_request *req)
> i915_gem_object_ggtt_unpin(from->legacy_hw_ctx.rcs_state);
> i915_gem_context_unreference(from);
> }
> -
> - uninitialized = !to->legacy_hw_ctx.initialized;
> - to->legacy_hw_ctx.initialized = true;
> -
> -done:
> i915_gem_context_reference(to);
> engine->last_context = to;
>
> - if (uninitialized) {
> + /* GEN8 does *not* require an explicit reload if the PDPs have been
> + * setup, and we do not wish to move them.
> + */
> + if (needs_pd_load_post(to, hw_flags)) {
> + trace_switch_mm(engine, to);
> + ret = to->ppgtt->switch_mm(to->ppgtt, req);
> + /* The hardware context switch is emitted, but we haven't
> + * actually changed the state - so it's probably safe to bail
> + * here. Still, let the user know something dangerous has
> + * happened.
> + */
> + if (ret)
> + return ret;
> +
> + to->ppgtt->pd_dirty_rings &= ~(1 << RCS);
> + }
> + if (hw_flags & MI_FORCE_RESTORE)
> + to->ppgtt->pd_dirty_rings &= ~(1 << RCS);
> +
> + for (i = 0; i < MAX_L3_SLICES; i++) {
> + if (!(to->remap_slice & (1<<i)))
> + continue;
> +
> + ret = i915_gem_l3_remap(req, i);
> + if (ret)
> + return ret;
> +
> + to->remap_slice &= ~(1<<i);
> + }
> +
> + if (!to->legacy_hw_ctx.initialized) {
> if (engine->init_context) {
> ret = engine->init_context(req);
> if (ret)
> - DRM_ERROR("ring init context: %d\n", ret);
> + return ret;
> }
> + to->legacy_hw_ctx.initialized = true;
> }
>
> return 0;
>
> unpin_out:
> - if (engine->id == RCS)
> - i915_gem_object_ggtt_unpin(to->legacy_hw_ctx.rcs_state);
> + i915_gem_object_ggtt_unpin(to->legacy_hw_ctx.rcs_state);
> return ret;
> }
>
> @@ -853,7 +832,31 @@ int i915_switch_context(struct drm_i915_gem_request *req)
> return 0;
> }
>
> - return do_switch(req);
> + if (engine->id != RCS) {
> + struct intel_context *from = engine->last_context;
> + struct intel_context *to = req->ctx;
> +
> + if (to->ppgtt &&
> + (from != to ||
> + intel_engine_flag(engine) & to->ppgtt->pd_dirty_rings)) {
> + int ret;
> +
> + trace_switch_mm(engine, to);
> + ret = to->ppgtt->switch_mm(to->ppgtt, req);
> + if (ret)
> + return ret;
> +
> + to->ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
> + }
> +
> + if (from)
> + i915_gem_context_unreference(from);
> + i915_gem_context_reference(to);
> + engine->last_context = to;
> + return 0;
> + }
> +
> + return do_rcs_switch(req);
> }
>
> static bool contexts_enabled(struct drm_device *dev)
> --
> 2.8.0.rc3
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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