From abe7e2ca232f7f32c2393a776c7399e510fffce0 Mon Sep 17 00:00:00 2001
From: "NathanNeurotic (Ripto)"
 <109461996+NathanNeurotic@users.noreply.github.com>
Date: Mon, 20 Jul 2026 10:35:59 -0700
Subject: [PATCH] perf(vcd): stop re-equipping BDMA on every launch when the
 card already carries a driver pair

NathanNeurotic: "BDMA operations are overboard... especially when the user already has the right one
equipped. It feels like we are doing unnecessary over work, causing extended wait on game launch
(handing over to POPSTARTER waiting on unnecessary MC transfer method?)" -- and the 1.0.1 anchor:
MMCE VCD launches there were a dumb, fast handoff; everything slow is machinery we added in front.

THE TRAP: vcdReadBdmaMode() collapses "marker file ABSENT" into VCD_BDMA_FAT32. A card that already
has the right usbd.irx + usbhdfsd.irx pair but no bdma_config.txt (manual setup, or any install
predating the marker) therefore read as a MISMATCH -- and vcdEnsureBdmaForLaunch ran the FULL equip on
EVERY VCD launch: source-device module force-loads with bounded waits, POPS/ probes, two module copies
onto the memory card, and a marker write. That is the extended pre-handoff wait, and it also CLOBBERED
the user's manually-placed pair every launch.

FIX: new no-marker fast path. Marker absent + BOTH driver modules present on the card = a manually
managed pair -> trust it, touch nothing, hand off (1.0.1-style). An EXPLICIT different marker (a real
variant switch) or a missing/partial pair still does the copy work -- ONCE -- after which the marker
matches and every later launch takes the existing cheap path. Fast-path cost when it fires: ~4-5 mc
metadata ops, replacing bounded-wait module loads + 4 file copies.

Adversarially verified (SHIP): gate matrix walked (corrupt-marker self-heal survives; explicit-FAT32
marker still equips; partial pair still repairs; no-card unchanged); the Settings-screen equip path is
untouched (helper is static, sole call site is the launch prep); POSIX-only IO rule kept; no
interaction with the POPSTARTER net/SMB co-tenants.

KNOWN TRADE-OFF (deliberate, doctrine): a manual pair of the WRONG variant now launches uncorrected --
previously it was overwritten every launch. The modules carry no variant identity, so this is
undetectable without hashing; one Settings-screen equip writes the marker and restores auto-correction
forever. Also by design: the fast path writes NO marker (it cannot know which variant the pair is), so
Settings' BDMA MODE keeps showing FAT32 for manually-managed cards.

Builds clean (make opl.elf, exit 0). HW-pending: FifthFox/MMCE VCD launch time.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 src/vcdsupport.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/vcdsupport.c b/src/vcdsupport.c
index 2297b01235..b6c6d07f22 100644
--- a/src/vcdsupport.c
+++ b/src/vcdsupport.c
@@ -878,6 +878,38 @@ int vcdEquipBdma(int source, int mode, char *diag, int diagSize)
     return (mr != 0) ? mr : 0;
 }
 
+// 1.0.1-style fast path for the launch equip: a card with NO marker but BOTH driver modules present is
+// a pair the user (or an install predating the marker file) manages MANUALLY. vcdReadBdmaMode()
+// collapses "marker absent" into VCD_BDMA_FAT32, so before this check every launch on such a card read
+// as a MISMATCH and paid the FULL equip -- source-device module loads with bounded waits plus two module
+// copies onto the memory card -- on EVERY VCD launch (NathanNeurotic: "unnecessary over work... extended
+// wait on game launch... unnecessary MC transfer"). Trust the card and hand off. An EXPLICIT different
+// marker (a real variant switch, checked by the caller before this) or a missing/partial pair still does
+// the copy work -- ONCE -- after which the marker matches and every later launch takes the cheap path.
+static int vcdBdmaManualPairPresent(void)
+{
+    char mcDir[64];
+    char path[96];
+    int fd, i;
+
+    if (!vcdResolvePopstarterMc(mcDir, sizeof(mcDir)))
+        return 0;
+    snprintf(path, sizeof(path), "%s/%s", mcDir, VCD_BDMA_MARKER);
+    fd = open(path, O_RDONLY);
+    if (fd >= 0) {
+        close(fd);
+        return 0; // marker PRESENT -> its verdict stands (the caller already compared it)
+    }
+    for (i = 0; i < 2; i++) {
+        snprintf(path, sizeof(path), "%s/%s", mcDir, vcdBdmaModule[i]);
+        fd = open(path, O_RDONLY);
+        if (fd < 0)
+            return 0; // pair incomplete -> a real equip is useful work
+        close(fd);
+    }
+    return 1;
+}
+
 // Best-effort auto-equip of the device-matching BDMA driver before a VCD launch (POPSLoader's
 // ApplyBdmaMode parity). POPSTARTER does its OWN SifIopReset, then reloads its block-device drivers
 // from the FIXED memory-card files mc?:/POPSTARTER/usbd.irx + usbhdfsd.irx; equipping copies the
@@ -901,6 +933,8 @@ void vcdEnsureBdmaForLaunch(int source, int mode)
         return; // FAT32 / invalid -> POPSTARTER's built-in driver, nothing to equip
     if (vcdReadBdmaMode() == mode)
         return; // the matching variant is already on the card
+    if (vcdBdmaManualPairPresent())
+        return; // no marker but a full pair on the card -- manually managed; dumb 1.0.1-style handoff
 
     int er = vcdEquipBdma(source, mode, diag, sizeof(diag));
     if (er == 0)