On 7/28/2022 17:00, Ceraolo Spurio, Daniele wrote:
On 7/27/2022 7:42 PM, John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
When the KMD sends a CLIENT_RESET request to GuC (as part of the
suspend sequence), GuC will mark the CTB buffer as 'UNUSED'. If the
KMD then checked the CTB queue, it would see a non-zero status value
and report the buffer as corrupted.
Technically, no G2H messages should be received once the CLIENT_RESET
has been sent. However, if a context was outstanding on an engine then
it would get reset and a reset notification would be sent. So, don't
actually treat UNUSED as a catastrophic error. Just flag it up as
unexpected and keep going.
Given that we disable CTs right after sending the CLIENT_RESET, there
is only a small window for the kernel to receive a G2H interrupt
before we turn everything off. If we want to support catching
unexpected G2Hs coming at that time, maybe we should instead make sure
all CT messages (if any) have been processed before the disable. Not a
blocker for this patch, can be done as a follow-up.
Yeah, it gets messy. How do you check for messages in a CTB that is
already marked as 'do not touch me'? The current check for available
work (head != tail) is after the status check. This is specifically so
that we don't try to process corrupted messages in a corrupted buffer.
But by definition, if the send(CLIENT_RESEET) call has returned then the
status is already 'do not use'. Ideally, we would just want to flush out
any pending interrupts before turning interrupts off in the sanitise
code. But then, is there a race where the interrupt hasn't quite made it
far enough by that time? Do we need to stall for a bit? How long?
As noted, in the case where we actually hit the issue the interrupt
handler did get to run in the gap between sending the reset message and
turning off the i915 side of the CTB. So we are basically into windows
of opportunity and diminishing returns. Given that it is supposedly an
impossible situation anyway, I'm not sure it is worth putting a complex
solution in to solve. But yeah, can think more and maybe get some kind
of extra check in there as a follow up.
John.
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Daniele
Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
---
.../i915/gt/uc/abi/guc_communication_ctb_abi.h | 8 +++++---
drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 18 ++++++++++++++++--
2 files changed, 21 insertions(+), 5 deletions(-)
diff --git
a/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
b/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
index df83c1cc7c7a6..28b8387f97b77 100644
--- a/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
+++ b/drivers/gpu/drm/i915/gt/uc/abi/guc_communication_ctb_abi.h
@@ -37,6 +37,7 @@
* | | | - _`GUC_CTB_STATUS_OVERFLOW` = 1 (head/tail too
large) |
* | | | - _`GUC_CTB_STATUS_UNDERFLOW` = 2 (truncated
message) |
* | | | - _`GUC_CTB_STATUS_MISMATCH` = 4 (head/tail
modified) |
+ * | | | - _`GUC_CTB_STATUS_UNUSED` = 8 (CTB is not in
use) |
*
+---+-------+--------------------------------------------------------------+
* |...| | RESERVED =
MBZ |
*
+---+-------+--------------------------------------------------------------+
@@ -49,9 +50,10 @@ struct guc_ct_buffer_desc {
u32 tail;
u32 status;
#define GUC_CTB_STATUS_NO_ERROR 0
-#define GUC_CTB_STATUS_OVERFLOW (1 << 0)
-#define GUC_CTB_STATUS_UNDERFLOW (1 << 1)
-#define GUC_CTB_STATUS_MISMATCH (1 << 2)
+#define GUC_CTB_STATUS_OVERFLOW BIT(0)
+#define GUC_CTB_STATUS_UNDERFLOW BIT(1)
+#define GUC_CTB_STATUS_MISMATCH BIT(2)
+#define GUC_CTB_STATUS_UNUSED BIT(3)
u32 reserved[13];
} __packed;
static_assert(sizeof(struct guc_ct_buffer_desc) == 64);
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
index f01325cd1b625..11b5d4ddb19ce 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
@@ -816,8 +816,22 @@ static int ct_read(struct intel_guc_ct *ct,
struct ct_incoming_msg **msg)
if (unlikely(ctb->broken))
return -EPIPE;
- if (unlikely(desc->status))
- goto corrupted;
+ if (unlikely(desc->status)) {
+ u32 status = desc->status;
+
+ if (status & GUC_CTB_STATUS_UNUSED) {
+ /*
+ * Potentially valid if a CLIENT_RESET request resulted in
+ * contexts/engines being reset. But should never happen as
+ * no contexts should be active when CLIENT_RESET is sent.
+ */
+ CT_ERROR(ct, "Unexpected G2H after GuC has stopped!\n");
+ status &= ~GUC_CTB_STATUS_UNUSED;
+ }
+
+ if (status)
+ goto corrupted;
+ }
GEM_BUG_ON(head > size);
