From 603b30fd35c44c24ed0b644f56022a91219b21ca Mon Sep 17 00:00:00 2001
From: Luca Toniolo <10792599+grandixximo@users.noreply.github.com>
Date: Sun, 4 Oct 2026 21:10:36 +0800
Subject: [PATCH] hostmot2: use the H entry's pins for two-part sserial
 encoders

LBP_ENCODER_L entries get no HAL pins, but the two-part Fanuc encoder
reassembly fell through into the encoder body with whichever entry
completed the pair. When a format lists the H part before the L part
the body ran on the L entry's pins and dereferenced handles that were
never created. Redirect the body to the matching LBP_ENCODER_H
entry's pin set, and refuse the pair with an error when no H entry
exists.
---
 src/hal/drivers/mesa-hostmot2/sserial.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/hal/drivers/mesa-hostmot2/sserial.c b/src/hal/drivers/mesa-hostmot2/sserial.c
index d0030a214f3..f5d079b95b0 100644
--- a/src/hal/drivers/mesa-hostmot2/sserial.c
+++ b/src/hal/drivers/mesa-hostmot2/sserial.c
@@ -1866,6 +1866,25 @@ int hm2_sserial_read_pins(hm2_sserial_remote_t *chan){
                 if ( ! (h_flag && l_flag)){
                     break;
                 }
+                if (conf->DataType == LBP_ENCODER_L) {
+                    // LBP_ENCODER_L entries have no pins; the encoder body
+                    // below must run on the matching LBP_ENCODER_H entry's
+                    // pin set regardless of which entry completes the pair.
+                    int e;
+                    for (e = 0; e < chan->num_confs; e++){
+                        if (chan->confs[e].DataType == LBP_ENCODER_H){
+                            pin = &chan->pins[e];
+                            break;
+                        }
+                    }
+                    if (e == chan->num_confs){
+                        HM2_ERR_NO_LL("sserial read: LBP_ENCODER_L with no matching LBP_ENCODER_H (name: ""%s"")\n",
+                                      conf->NameString);
+                        h_flag = 0; l_flag = 0;
+                        buff_store = 0;
+                        break;
+                    }
+                }
                 buff = buff_store;
                 /* Fallthrough */
             case LBP_ENCODER: