From 9beba08897c7cb8648e6ee471e3069dfa4a09609 Mon Sep 17 00:00:00 2001
From: Robert Zieba <robertzieba@microsoft.com>
Date: Wed, 11 Nov 2026 16:07:48 -0700
Subject: [PATCH] tcpm-service/ucsi: Fix GET_CAM_SUPPORTED data len

---
 Cargo.lock                       |  2 +-
 tcpm-service/src/service/ucsi.rs | 89 ++++++++++++++++++++++++++++----
 2 files changed, 79 insertions(+), 12 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 82f5815c..b5a9ec1b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -823,7 +823,7 @@ dependencies = [
 [[package]]
 name = "embedded-usb-pd"
 version = "0.1.0"
-source = "git+https://github.com/OpenDevicePartnership/embedded-usb-pd#a9088fc8549068c033cb4587b604b2573682dbf1"
+source = "git+https://github.com/OpenDevicePartnership/embedded-usb-pd#9a085ffcd376ea90a13daf04409af6b0a8a1f722"
 dependencies = [
  "bitfield 0.19.4",
  "bytemuck",
diff --git a/tcpm-service/src/service/ucsi.rs b/tcpm-service/src/service/ucsi.rs
index feab7530..1deee643 100644
--- a/tcpm-service/src/service/ucsi.rs
+++ b/tcpm-service/src/service/ucsi.rs
@@ -1,5 +1,6 @@
 use embedded_services::sync::Lockable;
 use embedded_services::warn;
+use embedded_usb_pd::LocalPortId;
 use embedded_usb_pd::ucsi::ConnectorNumber as _;
 use embedded_usb_pd::ucsi::MapPort as _;
 use embedded_usb_pd::ucsi::v1_2::cci::{Cci, GlobalCci};
@@ -28,6 +29,23 @@ pub struct UcsiResponse {
     pub data: Result<Option<ucsi::ResponseData>, PdError>,
 }
 
+/// LPM command response
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub struct LpmResponse {
+    pub data: Option<lpm::ResponseData>,
+    pub data_len_override: Option<usize>,
+}
+
+impl LpmResponse {
+    pub fn from_data(data: Option<lpm::ResponseData>) -> Self {
+        Self {
+            data,
+            data_len_override: None,
+        }
+    }
+}
+
 /// UCSI state
 #[derive(Default)]
 pub(super) struct State {
@@ -107,10 +125,42 @@ impl<'port, Reg: Registration<'port>> Service<'port, Reg> {
         }
     }
 
-    async fn process_lpm_command(
+    async fn get_alternate_modes_count(
         &mut self,
-        command: &ucsi::lpm::GlobalCommand,
-    ) -> Result<Option<lpm::ResponseData>, PdError> {
+        local_id: LocalPortId,
+        port: &mut <Reg::Port as Lockable>::Inner,
+    ) -> Result<usize, PdError> {
+        let mut offset = 0;
+        let mut total = 0;
+        loop {
+            let Some(lpm::ResponseData::GetAlternateModes(response)) = port
+                .execute_lpm_command(lpm::Command::new(lpm::CommandData::GetAlternateModes(
+                    lpm::get_alternate_modes::Args {
+                        connector_number: local_id,
+                        recipient: lpm::Recipient::Connector,
+                        mode_offset: offset,
+                        num_modes: 2,
+                    },
+                )))
+                .await?
+            else {
+                error!("({}): Received invalid response for GET_ALTERNATE_MODES", port.name());
+                return Err(PdError::InvalidResponse);
+            };
+
+            total += response.alt_modes.len();
+            offset += response.alt_modes.len() as u8;
+
+            // No more alt modes to fetch
+            if response.alt_modes.len() < lpm::get_alternate_modes::ALT_MODES_LEN {
+                break;
+            }
+        }
+
+        Ok(total)
+    }
+
+    async fn process_lpm_command(&mut self, command: &ucsi::lpm::GlobalCommand) -> Result<LpmResponse, PdError> {
         debug!("Processing LPM command: {:?}", command);
         let global_port_id = command.connector_number();
         let mut port = self.lookup_port(global_port_id)?.lock().await;
@@ -124,9 +174,13 @@ impl<'port, Reg: Registration<'port>> Service<'port, Reg> {
             lpm::CommandData::GetConnectorCapability(_) => {
                 // Override the capabilities if present in the config
                 if let Some(capabilities) = &self.config.ucsi_port_capabilities {
-                    Ok(Some(lpm::ResponseData::GetConnectorCapability(*capabilities)))
+                    Ok(LpmResponse::from_data(Some(lpm::ResponseData::GetConnectorCapability(
+                        *capabilities,
+                    ))))
                 } else {
-                    port.execute_lpm_command(local_command).await
+                    port.execute_lpm_command(local_command)
+                        .await
+                        .map(LpmResponse::from_data)
                 }
             }
             lpm::CommandData::GetConnectorStatus(_) => {
@@ -147,9 +201,21 @@ impl<'port, Reg: Registration<'port>> Service<'port, Reg> {
                     states_change.battery_charging_status_change = battery_charging_status.is_some();
                 }
 
-                response
+                response.map(LpmResponse::from_data)
             }
-            _ => port.execute_lpm_command(local_command).await,
+            lpm::CommandData::GetCamSupported(_) => {
+                let alt_modes_count = self.get_alternate_modes_count(local_port_id, &mut port).await?;
+
+                port.execute_lpm_command(local_command).await.map(|data| LpmResponse {
+                    data,
+                    // Calculation from UCSI spec
+                    data_len_override: Some((alt_modes_count % 8) + 1),
+                })
+            }
+            _ => port
+                .execute_lpm_command(local_command)
+                .await
+                .map(LpmResponse::from_data),
         }
     }
 
@@ -237,10 +303,11 @@ impl<'port, Reg: Registration<'port>> Service<'port, Reg> {
                                     .map(|inner| inner.map(ResponseData::Ppm));
                             }
                             ucsi::GlobalCommand::LpmCommand(lpm_command) => {
-                                response.data = self
-                                    .process_lpm_command(lpm_command)
-                                    .await
-                                    .map(|inner| inner.map(ResponseData::Lpm));
+                                let lpm_response = self.process_lpm_command(lpm_command).await;
+                                response.data = lpm_response.map(|inner| inner.data.map(ResponseData::Lpm));
+                                if let Ok(Some(data_len_override)) = lpm_response.map(|inner| inner.data_len_override) {
+                                    response.cci.data_len = data_len_override as u8;
+                                }
                             }
                         }