[PATCH 02/10] drm/i915/gt: Poison residual state [HWSP] across resume.

[Chris Wilson]

Since we may lose the content of any buffer when we relinquish control
of the system (e.g. suspend/resume), we have to be careful not to rely
on regaining control. A good method to detect when we might be using
garbage is by always injecting that garbage prior to first use on
load/resume/etc.

Suggested-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Venkata Ramana Nayana <venkata.ramana.nayana at intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 34f67eb9bfa1..7b3eaa1148df 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -3647,9 +3647,37 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
 			       &execlists->csb_status[reset_value]);
 }
 
+static void timeline_reset_seqno(const struct intel_timeline *tl)
+{
+	/* Must be pinned to be writable, and no requests in flight. */
+	GEM_BUG_ON(!atomic_read(&tl->pin_count));
+	GEM_BUG_ON(atomic_read(&tl->active_count));
+
+	WRITE_ONCE(*(u32 *)tl->hwsp_seqno, tl->seqno);
+}
+
 static void execlists_sanitize(struct intel_engine_cs *engine)
 {
+	/*
+	 * Poison residual state on resume, in case the suspend didn't!
+	 *
+	 * We have to assume that across suspend/resume (or other loss
+	 * of control) that the contents of our pinned buffers has been
+	 * lost, replaced by garbage. Since this doesn't always happen,
+	 * let's poison such state so that we more quickly spot when
+	 * we falsely assume it has been preserved.
+	 */
+	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
+		memset(engine->status_page.addr, POISON_INUSE, PAGE_SIZE);
+
 	reset_csb_pointers(engine);
+
+	/*
+	 * The kernel_context HWSP is stored in the status_page. As above,
+	 * that may be lost on resume/initialisation, and so we need to
+	 * reset the value in the HWSP.
+	 */
+	timeline_reset_seqno(engine->kernel_context->timeline);
 }
 
 static void enable_error_interrupt(struct intel_engine_cs *engine)
-- 
2.20.1