Re: [PATCH 1/1] drm/dp_mst: Kill the second sideband tx slot, save the world
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This commit has been processed because it contains a "Fixes:" tag
fixing commit: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper
(v0.6)").
The bot has tested the following trees: v5.6.7, v5.4.35, v4.19.118, v4.14.177,
v4.9.220, v4.4.220.
v5.6.7: Failed to apply! Possible dependencies:
1cfff5f01563 ("drm/dp_mst: Convert
drm_dp_mst_topology_mgr.is_waiting_for_dwn_reply to bitfield")
v5.4.35: Failed to apply! Possible dependencies:
14692a3637d4 ("drm/dp_mst: Add probe_lock")
2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + selftests")
37dfdc55ffeb ("drm/dp_mst: Cleanup drm_dp_send_link_address() a bit")
50094b5dcd32 ("drm/dp_mst: Destroy topology_mgr mutexes")
5950f0b797fc ("drm/dp_mst: Move link address dumping into a function")
5a64967a2f3b ("drm/dp_mst: Have DP_Tx send one msg at a time")
60f9ae9d0d3d ("drm/dp_mst: Remove huge conditional in
drm_dp_mst_handle_up_req()")
7cb12d48314e ("drm/dp_mst: Destroy MSTBs asynchronously")
7cbce45d6243 ("drm/dp_mst: Move test_calc_pbn_mode() into an actual
selftest")
8b1e589d138c ("drm/dp_mst: Refactor drm_dp_mst_handle_down_rep()")
9408cc94eb04 ("drm/dp_mst: Handle UP requests asynchronously")
a29d881875fc ("drm/dp_mst: Refactor drm_dp_mst_handle_up_req()")
caf81ec6cd72 ("drm: Destroy the correct mutex name in
drm_dp_mst_topology_mgr_destroy")
e2839ff692c6 ("drm/dp_mst: Rename drm_dp_add_port and drm_dp_update_port")
v4.19.118: Failed to apply! Possible dependencies:
16bff572cc66 ("drm/dp-mst-helper: Remove hotplug callback")
19b85cfabf5c ("drm/bochs: move remaining fb bits to kms")
2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + selftests")
2f69deb1d9a1 ("drm/arcpgu: prepare for drmP.h removal from
drm_modeset_helper.h")
48b442238250 ("drm/bochs: fix DRM_FORMAT_* handling for big endian
machines.")
562836a269e3 ("drm/dp_mst: Enable registration of AUX devices for MST
ports")
580fc13f3ee4 ("drm/dp: drmP.h include removal")
5a64967a2f3b ("drm/dp_mst: Have DP_Tx send one msg at a time")
6579c39594ae ("drm/bochs: atomic: switch planes to atomic, wire up
helpers.")
6abb49402a79 ("drm/bridge: cdns: prepare for drmP.h removal from
drm_modeset_helper.h")
6c76c0eb031f ("drm/bridge: ti-sn65dsi86: Fixup register names")
7780eb9ce80f ("bochs: convert to drm_dev_register")
86351de023dd ("drm/bochs: support changing byteorder at mode set time")
a095f15c00e2 ("drm/bridge: add support for sn65dsi86 bridge driver")
b814ec6d4535 ("drm/bridge: ti-sn65dsi86: Implement AUX channel")
df2052cc9221 ("bochs: convert to drm_fb_helper_fbdev_setup/teardown")
f38b7cca6d0e ("drm/bridge: tc358764: Add DSI to LVDS bridge driver")
fcd70cd36b9b ("drm: Split out drm_probe_helper.h")
fe1f664a3609 ("drm/arc: do not rely on drmP.h from drm_gem_cma_helper.h")
v4.14.177: Failed to apply! Possible dependencies:
1b0c0f9dc5ca ("drm/amdgpu: move userptr BOs to CPU domain during CS v2")
1ed3d2567c80 ("drm/amdgpu: keep the MMU lock until the update ends v4")
2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + selftests")
3fe89771cb0a ("drm/amdgpu: stop reserving the BO in the MMU callback v3")
4562236b3bc0 ("drm/amd/dc: Add dc display driver (v2)")
562836a269e3 ("drm/dp_mst: Enable registration of AUX devices for MST
ports")
580fc13f3ee4 ("drm/dp: drmP.h include removal")
5a64967a2f3b ("drm/dp_mst: Have DP_Tx send one msg at a time")
60de1c1740f3 ("drm/amdgpu: use a rw_semaphore for MMU notifiers")
9a18999640fa ("drm/amdgpu: move MMU notifier related defines to
amdgpu_mn.h")
9cca0b8e5df0 ("drm/amdgpu: move amdgpu_cs_sysvm_access_required into
find_mapping")
a216ab09955d ("drm/amdgpu: fix userptr put_page handling")
b72cf4fca2bb ("drm/amdgpu: move taking mmap_sem into get_user_pages v2")
ca666a3c298f ("drm/amdgpu: stop using BO status for user pages")
fcd70cd36b9b ("drm: Split out drm_probe_helper.h")
v4.9.220: Failed to apply! Possible dependencies:
178e32c224d2 ("drm/atomic: Remove pointless private object NULL state
check")
1cec20f0ea0e ("dma-buf: Restart reservation_object_wait_timeout_rcu() after
writes")
2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + selftests")
3941dae15ed9 ("drm_dp_aux_dev: switch to read_iter/write_iter")
3f3353b7e121 ("drm/dp: Introduce MST topology state to track available link
bandwidth")
562836a269e3 ("drm/dp_mst: Enable registration of AUX devices for MST
ports")
580fc13f3ee4 ("drm/dp: drmP.h include removal")
5a64967a2f3b ("drm/dp_mst: Have DP_Tx send one msg at a time")
6806cdf9aa1c ("drm/kms-helpers: Use recommened kerneldoc for struct member
refs")
78010cd9736e ("dma-buf/fence: add an lockdep_assert_held()")
9498c19b3f53 ("drm: Move tile group code into drm_connector.c")
9a83a71ac0d5 ("drm/fences: add DOC: for
[PATCH 1/1] drm/dp_mst: Kill the second sideband tx slot, save the world
While we support using both tx slots for sideband transmissions, it
appears that DisplayPort devices in the field didn't end up doing a very
good job of supporting it. From section 5.2.1 of the DP 2.0
specification:
There are MST Sink/Branch devices in the field that do not handle
interleaved message transactions.
To facilitate message transaction handling by downstream devices, an
MST Source device shall generate message transactions in an atomic
manner (i.e., the MST Source device shall not concurrently interleave
multiple message transactions). Therefore, an MST Source device shall
clear the Message_Sequence_No value in the Sideband_MSG_Header to 0.
This might come as a bit of a surprise since the vast majority of hubs
will support using both tx slots even if they don't support interleaved
message transactions, and we've also been using both tx slots since MST
was introduced into the kernel.
However, there is one device we've had trouble getting working
consistently with MST for so long that we actually assumed it was just
broken: the infamous Dell P2415Qb. Previously this monitor would appear
to work sometimes, but in most situations would end up timing out
LINK_ADDRESS messages almost at random until you power cycled the whole
display. After reading section 5.2.1 in the DP 2.0 spec, some closer
investigation into this infamous display revealed it was only ever
timing out on sideband messages in the second TX slot.
Sure enough, avoiding the second TX slot has suddenly made this monitor
function perfectly for the first time in five years. And since they
explicitly mention this in the specification, I doubt this is the only
monitor out there with this issue. This might even explain explain the
seemingly harmless garbage sideband responses we would occasionally see
with MST hubs!
So - rewrite our sideband TX handlers to only support one TX slot. In
order to simplify our sideband handling now that we don't support
transmitting to multiple MSTBs at once, we also move all state tracking
for down replies from mstbs to the topology manager.
Signed-off-by: Lyude Paul
Fixes: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper (v0.6)")
Cc: Sean Paul
Cc: "Lin, Wayne"
Cc: # v3.17+
Reviewed-by: Sean Paul
Link:
https://patchwork.freedesktop.org/patch/msgid/20200424181308.770749-1-ly...@redhat.com
---
drivers/gpu/drm/drm_dp_mst_topology.c | 122 +++---
include/drm/drm_dp_mst_helper.h | 18 +---
2 files changed, 33 insertions(+), 107 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 9d89ebf3a749..ed6faaf4bbf3 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1203,16 +1203,8 @@ static int drm_dp_mst_wait_tx_reply(struct
drm_dp_mst_branch *mstb,
/* remove from q */
if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED ||
- txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND) {
+ txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND)
list_del(>next);
- }
-
- if (txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
- txmsg->state == DRM_DP_SIDEBAND_TX_SENT) {
- mstb->tx_slots[txmsg->seqno] = NULL;
- }
- mgr->is_waiting_for_dwn_reply = false;
-
}
out:
if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
@@ -2691,22 +2683,6 @@ static int set_hdr_from_dst_qlock(struct
drm_dp_sideband_msg_hdr *hdr,
struct drm_dp_mst_branch *mstb = txmsg->dst;
u8 req_type;
- /* both msg slots are full */
- if (txmsg->seqno == -1) {
- if (mstb->tx_slots[0] && mstb->tx_slots[1]) {
- DRM_DEBUG_KMS("%s: failed to find slot\n", __func__);
- return -EAGAIN;
- }
- if (mstb->tx_slots[0] == NULL && mstb->tx_slots[1] == NULL) {
- txmsg->seqno = mstb->last_seqno;
- mstb->last_seqno ^= 1;
- } else if (mstb->tx_slots[0] == NULL)
- txmsg->seqno = 0;
- else
- txmsg->seqno = 1;
- mstb->tx_slots[txmsg->seqno] = txmsg;
- }
-
req_type = txmsg->msg[0] & 0x7f;
if (req_type == DP_CONNECTION_STATUS_NOTIFY ||
req_type == DP_RESOURCE_STATUS_NOTIFY)
@@ -2718,7 +2694,7 @@ static int set_hdr_from_dst_qlock(struct
drm_dp_sideband_msg_hdr *hdr,
hdr->lcr = mstb->lct - 1;
if (mstb->lct > 1)
memcpy(hdr->rad, mstb->rad, mstb->lct / 2);
- hdr->seqno = txmsg->seqno;
+
return 0;
}
/*
@@ -2733,15 +2709,15 @@ static int process_single_tx_qlock(struct
drm_dp_mst_topology_mgr *mgr,
int len, space, idx, tosend;
int ret;
+ if (txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
+
