From f229f28b8dd9372374138353d3cd2ba6afc4602a Mon Sep 17 00:00:00 2001
From: Sebastian Urban <surban@surban.net>
Date: Thu, 9 Nov 2023 21:02:31 +0100
Subject: [PATCH] Use old value for bcdVersion of OS descriptor.

Older kernels only accept this old, incorrect value.
Fixed kernels accept both value.
---
 .gitignore                 |  1 +
 src/function/custom/ffs.rs | 11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/.gitignore b/.gitignore
index 4fffb2f..dfef2f1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /target
 /Cargo.lock
+.cargo/config.toml
diff --git a/src/function/custom/ffs.rs b/src/function/custom/ffs.rs
index 8b4162d..eef0b2c 100644
--- a/src/function/custom/ffs.rs
+++ b/src/function/custom/ffs.rs
@@ -331,6 +331,13 @@ impl InterfaceAssocDesc {
     }
 }
 
+/// bcdVersion of OS descriptor.
+///
+/// This should actually be 0x0100, but due to a bug in older kernels they only accept
+/// 0x0001 as a valid value. Fixed kernels accepts both values. For the sake of
+/// compatibility keep the old, incorrect value.
+const OS_DESC_BCD_VERSION: u16 = 0x0001;
+
 #[derive(Clone, Debug)]
 pub struct OsDesc {
     pub interface: u8,
@@ -361,7 +368,7 @@ impl OsDescExt {
     fn write(&self, data: &mut Vec<u8>) -> Result<()> {
         match self {
             Self::ExtCompat(compats) => {
-                data.write_u16::<LE>(0x0100)?; // bcdVersion
+                data.write_u16::<LE>(OS_DESC_BCD_VERSION)?; // bcdVersion
                 data.write_u16::<LE>(4)?; // wIndex
                 data.write_u8(compats.len().try_into()?)?;
                 data.write_u8(0)?;
@@ -371,7 +378,7 @@ impl OsDescExt {
                 }
             }
             Self::ExtProp(props) => {
-                data.write_u16::<LE>(0x0100)?; // bcdVersion
+                data.write_u16::<LE>(OS_DESC_BCD_VERSION)?; // bcdVersion
                 data.write_u16::<LE>(5)?; // wIndex
                 data.write_u16::<LE>(props.len().try_into()?)?;