From cd9b225e3903f6993fe41fb32c5f95844f85098c Mon Sep 17 00:00:00 2001
From: vasilito <adminpupkin@gmail.com>
Date: Mon, 20 Jul 2026 19:27:00 +0900
Subject: [PATCH] =?UTF-8?q?docs:=20scope=20USB=20P7-B=20=E2=80=94=20real?=
 =?UTF-8?q?=20work=20is=20SEL/PEL=20timeout=20computation,=20not=20registe?=
 =?UTF-8?q?r=20writes?=
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Upstream xhci_calculate_lpm_timeout needs SuperSpeed endpoint companion
SEL/PEL parsing across the hub tree + tier policy + XHCI_LPM_SUPPORT
vendor quirk. Defaults-only timeout writes would be speculative and can
break device links. P7-B assigned a dedicated workstream.
---
 local/docs/USB-IMPLEMENTATION-PLAN.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/local/docs/USB-IMPLEMENTATION-PLAN.md b/local/docs/USB-IMPLEMENTATION-PLAN.md
index f46fe4975d..80a129ced3 100644
--- a/local/docs/USB-IMPLEMENTATION-PLAN.md
+++ b/local/docs/USB-IMPLEMENTATION-PLAN.md
@@ -699,6 +699,18 @@ defensive LPM clear runs on USB2 ports at attach when unsupported.
 
 **Reference:** `linux-7.1/drivers/usb/host/xhci-port.h:17-30`, `xhci.c:2800+` `xhci_stop_device()`.
 
+**Scoping audit (2026-07-20):** U1/U2 timeout *register* programming is trivial
+(xhci-hub.c:1488-1510, `PORT_U1/U2_TIMEOUT` in PORTPMSC), but the real work is
+upstream's timeout *computation*: `xhci_calculate_lpm_timeout` requires
+per-endpoint SEL/PEL from SuperSpeed endpoint companion descriptors across the
+hub tree, `calculate_max_exit_latency`, `xhci_check_tier_policy`, and only
+engages for controllers carrying the `XHCI_LPM_SUPPORT` quirk (vendor
+whitelist — "don't enable hub-initiated timeouts unless the vendor has
+provided information about their timeout algorithm"). A defaults-only
+implementation would be speculative non-upstream behavior that can break
+device links on real hardware. P7-B therefore needs a dedicated workstream
+covering endpoint-companion parsing + SEL/PEL plumbing first.
+
 **Tasks:**
 
 1. Implement U1/U2 entry per port via `PORT_U1_TIMEOUT` / `PORT_U2_TIMEOUT` registers.