[Intel-gfx] [PATCH 14/51] drm/i915/guc: Ensure G2H response has space in buffer

Matthew Brost
2021-07-16T20:00:18Z

Ensure G2H response has space in the buffer before sending H2G CTB as
the GuC can't handle any backpressure on the G2H interface.

v2:
(Matthew)
- s/INTEL_GUC_SEND/INTEL_GUC_CT_SEND
v3:
(Matthew)
- Add G2H credit accounting to blocking path, add g2h_release_space
helper
(John H)
- CTB_G2H_BUFFER_SIZE / 4 == G2H_ROOM_BUFFER_SIZE

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
---
drivers/gpu/drm/i915/gt/uc/intel_guc.h | 8 +-
drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 91 +++++++++++++++----
drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h | 9 +-
drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h | 4 +
.../gpu/drm/i915/gt/uc/intel_guc_submission.c | 13 ++-
5 files changed, 99 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
index 03b7222b04a2..80b88bae5f24 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
@@ -96,10 +96,11 @@ inline int intel_guc_send(struct intel_guc *guc, const u32 *action, u32 len)
}

static
-inline int intel_guc_send_nb(struct intel_guc *guc, const u32 *action, u32 len)
+inline int intel_guc_send_nb(struct intel_guc *guc, const u32 *action, u32 len,
+ u32 g2h_len_dw)
{
return intel_guc_ct_send(&guc->ct, action, len, NULL, 0,
- INTEL_GUC_CT_SEND_NB);
+ MAKE_SEND_FLAGS(g2h_len_dw));
}

static inline int
@@ -113,6 +114,7 @@ intel_guc_send_and_receive(struct intel_guc *guc, const u32 *action, u32 len,
static inline int intel_guc_send_busy_loop(struct intel_guc* guc,
const u32 *action,
u32 len,
+ u32 g2h_len_dw,
bool loop)
{
int err;
@@ -123,7 +125,7 @@ static inline int intel_guc_send_busy_loop(struct intel_guc* guc,
might_sleep_if(loop && not_atomic);

retry:
- err = intel_guc_send_nb(guc, action, len);
+ err = intel_guc_send_nb(guc, action, len, g2h_len_dw);
if (unlikely(err == -EBUSY && loop)) {
if (likely(not_atomic)) {
if (msleep_interruptible(sleep_period_ms))
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 019b25ff1888..c33906ec478d 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
@@ -73,6 +73,7 @@ static inline struct drm_device *ct_to_drm(struct intel_guc_ct *ct)
#define CTB_DESC_SIZE ALIGN(sizeof(struct guc_ct_buffer_desc), SZ_2K)
#define CTB_H2G_BUFFER_SIZE (SZ_4K)
#define CTB_G2H_BUFFER_SIZE (4 * CTB_H2G_BUFFER_SIZE)
+#define G2H_ROOM_BUFFER_SIZE (CTB_G2H_BUFFER_SIZE / 4)

struct ct_request {
struct list_head link;
@@ -129,23 +130,27 @@ static void guc_ct_buffer_desc_init(struct guc_ct_buffer_desc *desc)

static void guc_ct_buffer_reset(struct intel_guc_ct_buffer *ctb)
{
+ u32 space;
+
ctb->broken = false;
ctb->tail = 0;
ctb->head = 0;
- ctb->space = CIRC_SPACE(ctb->tail, ctb->head, ctb->size);
+ space = CIRC_SPACE(ctb->tail, ctb->head, ctb->size) - ctb->resv_space;
+ atomic_set(&ctb->space, space);

guc_ct_buffer_desc_init(ctb->desc);
}

static void guc_ct_buffer_init(struct intel_guc_ct_buffer *ctb,
struct guc_ct_buffer_desc *desc,
- u32 *cmds, u32 size_in_bytes)
+ u32 *cmds, u32 size_in_bytes, u32 resv_space)
{
GEM_BUG_ON(size_in_bytes % 4);

ctb->desc = desc;
ctb->cmds = cmds;
ctb->size = size_in_bytes / 4;
+ ctb->resv_space = resv_space / 4;

guc_ct_buffer_reset(ctb);
}
@@ -226,6 +231,7 @@ int intel_guc_ct_init(struct intel_guc_ct *ct)
struct guc_ct_buffer_desc *desc;
u32 blob_size;
u32 cmds_size;
+ u32 resv_space;
void *blob;
u32 *cmds;
int err;
@@ -250,19 +256,23 @@ int intel_guc_ct_init(struct intel_guc_ct *ct)
desc = blob;
cmds = blob + 2 * CTB_DESC_SIZE;
cmds_size = CTB_H2G_BUFFER_SIZE;
- CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u\n", "send",
- ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
+ resv_space = 0;
+ CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u/%u\n", "send",
+ ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size,
+ resv_space);

- guc_ct_buffer_init(&ct->ctbs.send, desc, cmds, cmds_size);
+ guc_ct_buffer_init(&ct->ctbs.send, desc, cmds, cmds_size, resv_space);

/* store pointers to desc and cmds for recv ctb */
desc = blob + CTB_DESC_SIZE;
cmds = blob + 2 * CTB_DESC_SIZE + CTB_H2G_BUFFER_SIZE;
cmds_size = CTB_G2H_BUFFER_SIZE;
- CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u\n", "recv",
- ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
+ resv_space = G2H_ROOM_BUFFER_SIZE;
+ CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u/%u\n", "recv",
+ ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size,
+ resv_space);

- guc_ct_buffer_init(&ct->ctbs.recv, desc, cmds, cmds_size);
+ guc_ct_buffer_init(&ct->ctbs.recv, desc, cmds, cmds_size, resv_space);

return 0;
}
@@ -461,8 +471,8 @@ static int ct_write(struct intel_guc_ct *ct,

/* update local copies */
ctb->tail = tail;
- GEM_BUG_ON(ctb->space < len + GUC_CTB_HDR_LEN);
- ctb->space -= len + GUC_CTB_HDR_LEN;
+ GEM_BUG_ON(atomic_read(&ctb->space) < len + GUC_CTB_HDR_LEN);
+ atomic_sub(len + GUC_CTB_HDR_LEN, &ctb->space);

/* now update descriptor */
WRITE_ONCE(desc->tail, tail);
@@ -537,6 +547,32 @@ static inline bool ct_deadlocked(struct intel_guc_ct *ct)
return ret;
}

+static inline bool g2h_has_room(struct intel_guc_ct *ct, u32 g2h_len_dw)
+{
+ struct intel_guc_ct_buffer *ctb = &ct->ctbs.recv;
+
+ /*
+ * We leave a certain amount of space in the G2H CTB buffer for
+ * unexpected G2H CTBs (e.g. logging, engine hang, etc...)
+ */
+ return !g2h_len_dw || atomic_read(&ctb->space) >= g2h_len_dw;
+}
+
+static inline void g2h_reserve_space(struct intel_guc_ct *ct, u32 g2h_len_dw)
+{
+ lockdep_assert_held(&ct->ctbs.send.lock);
+
+ GEM_BUG_ON(!g2h_has_room(ct, g2h_len_dw));
+
+ if (g2h_len_dw)
+ atomic_sub(g2h_len_dw, &ct->ctbs.recv.space);
+}
+
+static inline void g2h_release_space(struct intel_guc_ct *ct, u32 g2h_len_dw)
+{
+ atomic_add(g2h_len_dw, &ct->ctbs.recv.space);
+}
+
static inline bool h2g_has_room(struct intel_guc_ct *ct, u32 len_dw)
{
struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
@@ -544,7 +580,7 @@ static inline bool h2g_has_room(struct intel_guc_ct *ct, u32 len_dw)
u32 head;
u32 space;

- if (ctb->space >= len_dw)
+ if (atomic_read(&ctb->space) >= len_dw)
return true;

head = READ_ONCE(desc->head);
@@ -557,16 +593,16 @@ static inline bool h2g_has_room(struct intel_guc_ct *ct, u32 len_dw)
}

space = CIRC_SPACE(ctb->tail, head, ctb->size);
- ctb->space = space;
+ atomic_set(&ctb->space, space);

return space >= len_dw;
}

-static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
+static int has_room_nb(struct intel_guc_ct *ct, u32 h2g_dw, u32 g2h_dw)
{
lockdep_assert_held(&ct->ctbs.send.lock);

- if (unlikely(!h2g_has_room(ct, len_dw))) {
+ if (unlikely(!h2g_has_room(ct, h2g_dw) || !g2h_has_room(ct, g2h_dw))) {
if (ct->stall_time == KTIME_MAX)
ct->stall_time = ktime_get();

@@ -580,6 +616,9 @@ static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
return 0;
}

+#define G2H_LEN_DW(f) \
+ FIELD_GET(INTEL_GUC_CT_SEND_G2H_DW_MASK, f) ? \
+ FIELD_GET(INTEL_GUC_CT_SEND_G2H_DW_MASK, f) + GUC_CTB_HXG_MSG_MIN_LEN : 0
static int ct_send_nb(struct intel_guc_ct *ct,
const u32 *action,
u32 len,
@@ -587,12 +626,13 @@ static int ct_send_nb(struct intel_guc_ct *ct,
{
struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
unsigned long spin_flags;
+ u32 g2h_len_dw = G2H_LEN_DW(flags);
u32 fence;
int ret;

spin_lock_irqsave(&ctb->lock, spin_flags);

- ret = has_room_nb(ct, len + GUC_CTB_HDR_LEN);
+ ret = has_room_nb(ct, len + GUC_CTB_HDR_LEN, g2h_len_dw);
if (unlikely(ret))
goto out;

@@ -601,6 +641,7 @@ static int ct_send_nb(struct intel_guc_ct *ct,
if (unlikely(ret))
goto out;

+ g2h_reserve_space(ct, g2h_len_dw);
intel_guc_notify(ct_to_guc(ct));

out:
@@ -632,11 +673,13 @@ static int ct_send(struct intel_guc_ct *ct,
/*
* We use a lazy spin wait loop here as we believe that if the CT
* buffers are sized correctly the flow control condition should be
- * rare.
+ * rare. Reserving the maximum size in the G2H credits as we don't know
+ * how big the response is going to be.
*/
retry:
spin_lock_irqsave(&ctb->lock, flags);
- if (unlikely(!h2g_has_room(ct, len + GUC_CTB_HDR_LEN))) {
+ if (unlikely(!h2g_has_room(ct, len + GUC_CTB_HDR_LEN) ||
+ !g2h_has_room(ct, GUC_CTB_HXG_MSG_MAX_LEN))) {
if (ct->stall_time == KTIME_MAX)
ct->stall_time = ktime_get();
spin_unlock_irqrestore(&ctb->lock, flags);
@@ -664,6 +707,7 @@ static int ct_send(struct intel_guc_ct *ct,
spin_unlock(&ct->requests.lock);

err = ct_write(ct, action, len, fence, 0);
+ g2h_reserve_space(ct, GUC_CTB_HXG_MSG_MAX_LEN);

spin_unlock_irqrestore(&ctb->lock, flags);

@@ -673,6 +717,7 @@ static int ct_send(struct intel_guc_ct *ct,
intel_guc_notify(ct_to_guc(ct));

err = wait_for_ct_request_update(&request, status);
+ g2h_release_space(ct, GUC_CTB_HXG_MSG_MAX_LEN);
if (unlikely(err))
goto unlink;

@@ -992,10 +1037,22 @@ static void ct_incoming_request_worker_func(struct work_struct *w)
static int ct_handle_event(struct intel_guc_ct *ct, struct ct_incoming_msg *request)
{
const u32 *hxg = &request->msg[GUC_CTB_MSG_MIN_LEN];
+ u32 action = FIELD_GET(GUC_HXG_EVENT_MSG_0_ACTION, hxg[0]);
unsigned long flags;

GEM_BUG_ON(FIELD_GET(GUC_HXG_MSG_0_TYPE, hxg[0]) != GUC_HXG_TYPE_EVENT);

+ /*
+ * Adjusting the space must be done in IRQ or deadlock can occur as the
+ * CTB processing in the below workqueue can send CTBs which creates a
+ * circular dependency if the space was returned there.
+ */
+ switch (action) {
+ case INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_DONE:
+ case INTEL_GUC_ACTION_DEREGISTER_CONTEXT_DONE:
+ g2h_release_space(ct, request->size);
+ }
+
spin_lock_irqsave(&ct->requests.lock, flags);
list_add_tail(&request->link, &ct->requests.incoming);
spin_unlock_irqrestore(&ct->requests.lock, flags);
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
index edd1bba0445d..785dfc5c6efb 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
@@ -33,6 +33,7 @@ struct intel_guc;
* @desc: pointer to the buffer descriptor
* @cmds: pointer to the commands buffer
* @size: size of the commands buffer in dwords
+ * @resv_space: reserved space in buffer in dwords
* @head: local shadow copy of head in dwords
* @tail: local shadow copy of tail in dwords
* @space: local shadow copy of space in dwords
@@ -43,9 +44,10 @@ struct intel_guc_ct_buffer {
struct guc_ct_buffer_desc *desc;
u32 *cmds;
u32 size;
+ u32 resv_space;
u32 tail;
u32 head;
- u32 space;
+ atomic_t space;
bool broken;
};

@@ -97,6 +99,11 @@ static inline bool intel_guc_ct_enabled(struct intel_guc_ct *ct)
}

#define INTEL_GUC_CT_SEND_NB BIT(31)
+#define INTEL_GUC_CT_SEND_G2H_DW_SHIFT 0
+#define INTEL_GUC_CT_SEND_G2H_DW_MASK (0xff << INTEL_GUC_CT_SEND_G2H_DW_SHIFT)
+#define MAKE_SEND_FLAGS(len) \
+ ({GEM_BUG_ON(!FIELD_FIT(INTEL_GUC_CT_SEND_G2H_DW_MASK, len)); \
+ (FIELD_PREP(INTEL_GUC_CT_SEND_G2H_DW_MASK, len) | INTEL_GUC_CT_SEND_NB);})
int intel_guc_ct_send(struct intel_guc_ct *ct, const u32 *action, u32 len,
u32 *response_buf, u32 response_buf_size, u32 flags);
void intel_guc_ct_event_handler(struct intel_guc_ct *ct);
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
index 4e4edc368b77..94bb1ca6f889 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
@@ -17,6 +17,10 @@
#include "abi/guc_communication_ctb_abi.h"
#include "abi/guc_messages_abi.h"

+/* Payload length only i.e. don't include G2H header length */
+#define G2H_LEN_DW_SCHED_CONTEXT_MODE_SET 2
+#define G2H_LEN_DW_DEREGISTER_CONTEXT 1
+
#define GUC_CONTEXT_DISABLE 0
#define GUC_CONTEXT_ENABLE 1

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 4443cc6f5320..f7e34baa9506 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -260,6 +260,7 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
struct intel_context *ce = rq->context;
u32 action[3];
int len = 0;
+ u32 g2h_len_dw = 0;
bool enabled = context_enabled(ce);

GEM_BUG_ON(!atomic_read(&ce->guc_id_ref));
@@ -271,13 +272,13 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
action[len++] = GUC_CONTEXT_ENABLE;
set_context_pending_enable(ce);
intel_context_get(ce);
+ g2h_len_dw = G2H_LEN_DW_SCHED_CONTEXT_MODE_SET;
} else {
action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT;
action[len++] = ce->guc_id;
}

- err = intel_guc_send_nb(guc, action, len);
-
+ err = intel_guc_send_nb(guc, action, len, g2h_len_dw);
if (!enabled && !err) {
set_context_enabled(ce);
} else if (!enabled) {
@@ -730,7 +731,7 @@ static int __guc_action_register_context(struct intel_guc *guc,
offset,
};

- return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
+ return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), 0, true);
}

static int register_context(struct intel_context *ce)
@@ -750,7 +751,8 @@ static int __guc_action_deregister_context(struct intel_guc *guc,
guc_id,
};

- return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
+ return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action),
+ G2H_LEN_DW_DEREGISTER_CONTEXT, true);
}

static int deregister_context(struct intel_context *ce, u32 guc_id)
@@ -891,7 +893,8 @@ static void __guc_context_sched_disable(struct intel_guc *guc,

intel_context_get(ce);

- intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
+ intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action),
+ G2H_LEN_DW_SCHED_CONTEXT_MODE_SET, true);
}

static u16 prep_context_pending_disable(struct intel_context *ce)
--
2.28.0