Re: [PATCH] usb: gadget: f_fs: Fix kernel panic for SuperSpeed

From: Jim Lin
Date: Wed May 04 2016 - 04:07:55 EST

On 2016å04æ29æ 19:57, Felipe Balbi wrote:
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Jim Lin <jilin@xxxxxxxxxx> writes:
On 2016å04æ28æ 20:21, Felipe Balbi wrote:
I also attach git log of system/core/adb/usb_linux_client.cpp of Android
N for your reference.
Author: Badhri Jagan Sridharan <Badhri@xxxxxxxxxx>
Date: Mon Oct 5 13:04:03 2015 -0700

adbd: Add os descriptor support for adb.

Eventhough windows does not rely on extended os
descriptor for adbd, when android usb device is
configures as a composite device such as mtp+adb,
windows discards the extended os descriptor even
if one of the USB function fails to send
the extended compat descriptor. This results in automatic
install of MTP driverto fail when Android device is in
"File Transfer" mode with adb enabled.
Okay, cool. Can you check that you're limitting your controller's speed
to high-speed ?

Let's focus on original patch.
Could you help to explain why we need below d->Reserved1 checking?
Now the question is that

Page 7 of OS_Desc_CompatID.doc
defines reserved field to be 1 and
below code will think that os_desc is invalid because d->Reserved1 is 1.

In f_fs.c
static int __ffs_data_do_os_desc(enum ffs_os_desc_type type,
struct usb_os_desc_header *h, void *data,
unsigned len, void *priv)
struct ffs_data *ffs = priv;
u8 length;


switch (type) {
struct usb_ext_compat_desc *d = data;
int i;

if (len < sizeof(*d) ||
d->bFirstInterfaceNumber >= ffs->interfaces_count ||
return -EINVAL;
that's fine, but this is only failing because something else is
returning the wrong set of descriptors (SS vs HS). That's the bug we
want to fix, not work around it.