Currently, the USB gadget framework supports only version 1.0 of the MS OS
descriptor. OS desc has a field bcdVersion indicating its version, with
v1.0 represented by the value 0x100. However, __ffs_do_os_desc_header()
was expecting the incorrect value 0x1, so allow the correct value 0x100.
The bcdVersion field of the descriptor that is actually sent to the host
is set by composite_setup() (in composite.c) to the fixed value 0x100.
Therefore, it can be understood that __ffs_do_os_desc_header() is only
performing a format check of the OS desc passed to functionfs. If a value
other than 0x100 is accepted, there is no effect on communication over
the USB bus. Indeed, until now __ffs_do_os_desc_header() has only accepted
the incorrect value 0x1, but there was no problem with the communication
over the USB bus.
However, this can be confusing for functionfs userspace drivers. Since
bcdVersion=0x100 is used in actual communication, functionfs should accept
the value 0x100.
Note that the correct value for bcdVersion in OS desc v1.0 is 0x100, but
to avoid breaking old userspace drivers, the value 0x1 is also accepted as
an exception. At this time, a message is output to notify the user to fix
the userspace driver.
Signed-off-by: Yuta Hayama <hayama@xxxxxxxxxxx>
---
Changelog
v3:
- modify wording of pr_warn() message (thanks to Andrzej),
and remove unnecessary format specifier.
v2:
- remove comma inserted incorrectly in pr_vdebug()
- when bcd_version == 0x1, use pr_warn() instead of pr_vdebug()
drivers/usb/gadget/function/f_fs.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 8ad354741380..34ddb1802c5f 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2292,8 +2292,11 @@ static int __ffs_do_os_desc_header(enum ffs_os_desc_type *next_type,
u16 bcd_version = le16_to_cpu(desc->bcdVersion);
u16 w_index = le16_to_cpu(desc->wIndex);
- if (bcd_version != 1) {
- pr_vdebug("unsupported os descriptors version: %d",
+ if (bcd_version == 0x1) {
+ pr_warn("bcdVersion must be 0x0100, stored in Little Endian order. "
+ "Userspace driver should be fixed, accepting 0x0001 for compatibility.\n");
+ } else if (bcd_version != 0x100) {
+ pr_vdebug("unsupported os descriptors version: 0x%x\n",
bcd_version);
return -EINVAL;
}
--
2.25.1
