github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-11-07 06:17:02 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

i3c: master: allocate IBI workqueue with WQ_HIGHPRI

Browse Source 
The IBI (In-Band Interrupt) workqueue is allocated with only
WQ_MEM_RECLAIM, which places IBI payload processing at normal
worker priority. This is inadequate given the time-sensitive
nature of IBI handling.

In the I3C protocol, when a target asserts an IBI, the SDA line
is held low until the master acknowledges and completes the
exchange. The IRQ handler (top half) ACKs the IBI, reads the
payload, emits a STOP, and immediately queues the payload
processing to the per-device ordered workqueue via
i3c_master_queue_ibi() — effectively the bottom half of the
IBI interrupt path.

If this workqueue worker is delayed by competing normal-priority
tasks, the IBI notification reaches the client driver late. For
latency-sensitive clients (e.g. sensors reporting alerts,
hotplug events), this defeats the purpose of using IBI over
polling. Furthermore, because the ordered workqueue serialises
slots, a backlog of delayed slots can exhaust the pre-allocated
IBI slot pool, causing subsequent IBIs to be dropped at the
hardware level.

Add WQ_HIGHPRI to ensure IBI bottom-half work is scheduled
promptly after the top-half IRQ handler enqueues it, keeping
the IBI processing pipeline consistent with the interrupt-like
semantics the protocol demands.

Signed-off-by: Stanley Chu <yschu@nuvoton.com>
Acked-by: Mukesh Kumar Savaliya <mukesh.savaliya@oss.qualcomm.com>
Link: https://patch.msgid.link/20260810013059.3055787-1-yschu@nuvoton.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
This commit is contained in:
Stanley Chu 2026-08-10 09:30:59 +08:00 committed by Alexandre Belloni
parent cee9395acd
commit 591980aaaa
1 changed files with 2 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/i3c/master.c
View File

@ -3945,7 +3945,8 @@ int i3c_dev_request_ibi_locked(struct i3c_dev_desc *dev,
if (!ibi)
return -ENOMEM;
ibi->wq = alloc_ordered_workqueue(dev_name(i3cdev_to_dev(dev->dev)), WQ_MEM_RECLAIM);
ibi->wq = alloc_ordered_workqueue(dev_name(i3cdev_to_dev(dev->dev)),
WQ_MEM_RECLAIM | WQ_HIGHPRI);
if (!ibi->wq) {
kfree(ibi);
return -ENOMEM;