Trying to enable printk debugging for GEM is fraught with the issue of
spam; interactions with HW are very frequent and often boring. However,
one instance where they are not so boring is just before a BUG; here
ftrace provides a facility to dump its ringbuffer on an oops. So for CI
let's enable trace_printk() to capture the last exchanges with HW as a
death rattle.
For example,
[ 79.234110] ------------[ cut here ]------------
[ 79.234137] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:907!
[ 79.234145] invalid opcode: 0000 [#1] SMP
[ 79.234153] Dumping ftrace buffer:
[ 79.234158] ---------------------------------
...
[ 79.314044] gem_conc-1059 1..s1 79203443us : intel_lrc_irq_handler: bcs0 out[0]: ctx=5.2, seqno=145
[ 79.314089] gem_conc-1059 1..s. 79220800us : intel_lrc_irq_handler: bcs0 csb[1/1]: status=0x00000018:0x00000005
[ 79.314133] gem_conc-1059 1..s. 79220803us : intel_lrc_irq_handler: bcs0 out[0]: ctx=5.1, seqno=145
[ 79.314177] gem_conc-1062 2..s1 79230458us : intel_lrc_irq_handler: bcs0 in[0]: ctx=8.1, seqno=146
[ 79.314220] gem_conc-1062 2..s1 79230515us : intel_lrc_irq_handler: bcs0 in[0]: ctx=8.2, seqno=147
[ 79.314265] gem_conc-1059 1..s1 79230951us : intel_lrc_irq_handler: bcs0 csb[2/3]: status=0x00000012:0x00000008
[ 79.314309] gem_conc-1059 1..s1 79230954us : intel_lrc_irq_handler: bcs0 out[0]: ctx=8.2, seqno=147
[ 79.314353] gem_conc-1059 1..s1 79230954us : intel_lrc_irq_handler: bcs0 csb[3/3]: status=0x00008002:0x00000008
[ 79.314396] gem_conc-1059 1..s1 79230955us : intel_lrc_irq_handler: bcs0 out[0]: ctx=8.1, seqno=147
[ 79.314402] ---------------------------------
v2: Tweak the formatting to be more consistent between in/out.
v3: do {} while (0) stub macro protection
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/Kconfig.debug | 14 ++++++++++++++
drivers/gpu/drm/i915/i915_gem.h | 6 ++++++
drivers/gpu/drm/i915/intel_lrc.c | 17 +++++++++++++++++
3 files changed, 37 insertions(+)
diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
index 19c77c6feb24..9e53edbc713b 100644
--- a/drivers/gpu/drm/i915/Kconfig.debug
+++ b/drivers/gpu/drm/i915/Kconfig.debug
@@ -28,6 +28,7 @@ config DRM_I915_DEBUG
select SW_SYNC # signaling validation framework (igt/syncobj*)
select DRM_I915_SW_FENCE_DEBUG_OBJECTS
select DRM_I915_SELFTEST
+ select DRM_I915_TRACE_GEM
default n
help
Choose this option to turn on extra driver debugging that may affect
@@ -49,6 +50,19 @@ config DRM_I915_DEBUG_GEM
If in doubt, say "N".
+config DRM_I915_TRACE_GEM
+ bool "Insert extra ftrace output from the GEM internals"
+ select TRACING
+ default n
+ help
+ Enable additional and verbose debugging output that will spam
+ ordinary tests, but may be vital for post-mortem debugging when
+ used with /proc/sys/kernel/ftrace_dump_on_oops
+
+ Recommended for driver developers only.
+
+ If in doubt, say "N".
+
config DRM_I915_SW_FENCE_DEBUG_OBJECTS
bool "Enable additional driver debugging for fence objects"
depends on DRM_I915
diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
index ee54597465b6..ff42b5f0e981 100644
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -44,6 +44,12 @@
#define GEM_DEBUG_BUG_ON(expr)
#endif
+#if IS_ENABLED(CONFIG_DRM_I915_TRACE_GEM)
+#define GEM_TRACE(...) trace_printk(__VA_ARGS__)
+#else
+#define GEM_TRACE(...) do { } while (0)
+#endif
+
#define I915_NUM_ENGINES 5
#endif /* __I915_GEM_H__ */
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 6840ec8db037..020ca7c9c75f 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -466,6 +466,11 @@ static void execlists_submit_ports(struct intel_engine_cs *engine)
port_set(&port[n], port_pack(rq, count));
desc = execlists_update_context(rq);
GEM_DEBUG_EXEC(port[n].context_id = upper_32_bits(desc));
+
+ GEM_TRACE("%s in[%d]: ctx=%d.%d, seqno=%x\n",
+ engine->name, n,
+ rq->ctx->hw_id, count,
+ rq->global_seqno);
} else {
GEM_BUG_ON(!n);
desc = 0;
@@ -520,6 +525,7 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
ce->ring->tail &= (ce->ring->size - 1);
ce->lrc_reg_state[CTX_RING_TAIL+1] = ce->ring->tail;
+ GEM_TRACE("\n");
for (n = execlists_num_ports(&engine->execlists); --n; )
elsp_write(0, elsp);
@@ -832,6 +838,10 @@ static void intel_lrc_irq_handler(unsigned long data)
head = execlists->csb_head;
tail = READ_ONCE(buf[write_idx]);
}
+ GEM_TRACE("%s cs-irq head=%d [%d], tail=%d [%d]\n",
+ engine->name,
+ head, GEN8_CSB_READ_PTR(readl(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)))),
+ tail, GEN8_CSB_WRITE_PTR(readl(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)))));
while (head != tail) {
struct drm_i915_gem_request *rq;
@@ -859,6 +869,9 @@ static void intel_lrc_irq_handler(unsigned long data)
*/
status = READ_ONCE(buf[2 * head]); /* maybe mmio! */
+ GEM_TRACE("%s csb[%dd]: status=0x%08x:0x%08x\n",
+ engine->name, head,
+ status, buf[2*head + 1]);
if (!(status & GEN8_CTX_STATUS_COMPLETED_MASK))
continue;
@@ -886,6 +899,10 @@ static void intel_lrc_irq_handler(unsigned long data)
GEM_DEBUG_BUG_ON(buf[2 * head + 1] != port->context_id);
rq = port_unpack(port, &count);
+ GEM_TRACE("%s out[0]: ctx=%d.%d, seqno=%x\n",
+ engine->name,
+ rq->ctx->hw_id, count,
+ rq->global_seqno);
GEM_BUG_ON(count == 0);
if (--count == 0) {
GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
--
2.15.0
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