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

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Date:	Fri, 29 Apr 2016 19:27:30 +0800
From:	Jim Lin <jilin@...dia.com>
To:	Felipe Balbi <balbi@...nel.org>
CC:	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: f_fs: Fix kernel panic for SuperSpeed

On 2016年04月28日 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@...gle.com>
>> 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.
>>
>> https://msdn.microsoft.com/en-us/library/windows/hardware/gg463179.aspx
>> "
> 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

https://msdn.microsoft.com/en-us/library/windows/hardware/gg463179.aspx

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;

     ENTER();

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

         if (len < sizeof(*d) ||
             d->bFirstInterfaceNumber >= ffs->interfaces_count ||
             d->Reserved1)
             return -EINVAL;
"

--nvpublic