Re: [PATCH] drm/i915/guc: Use iosys_map interface to update lrc_desc

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On Tue, Mar 08, 2022 at 10:17:42PM +0530, Balasubramani Vivekanandan wrote:
This patch is continuation of the effort to move all pointers in i915,
which at any point may be pointing to device memory or system memory, to
iosys_map interface.
More details about the need of this change is explained in the patch
series which initiated this task
https://patchwork.freedesktop.org/series/99711/

This patch converts all access to the lrc_desc through iosys_map
interfaces.

Cc: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Cc: John Harrison <John.C.Harrison@xxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@xxxxxxxxx>
---

...

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
@@ -2245,13 +2256,13 @@ static void prepare_context_registration_info(struct intel_context *ce)
	GEM_BUG_ON(i915_gem_object_is_lmem(guc->ct.vma->obj) !=
		   i915_gem_object_is_lmem(ce->ring->vma->obj));

-	desc = __get_lrc_desc(guc, ctx_id);
-	desc->engine_class = engine_class_to_guc_class(engine->class);
-	desc->engine_submit_mask = engine->logical_mask;
-	desc->hw_context_desc = ce->lrc.lrca;
-	desc->priority = ce->guc_state.prio;
-	desc->context_flags = CONTEXT_REGISTRATION_FLAG_KMD;
-	guc_context_policy_init(engine, desc);
+	memset(&desc, 0, sizeof(desc));

previously we would re-use whatever was left in
guc->lrc_desc_pool_vaddr. Here we are changing it to always zero
everything and set the fields we are interested in.

As I'm not too familiar with this part and I see us traversing child guc_process_desc
which may point to the same id, it doesn't _feel_ safe. Did you check if
this is not zero'ing what it shouldn't?

Matt Brost / John / Daniele, could you clarify?

thanks
Lucas De Marchi



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