linux-kernel - Re: [PATCH 1/2] Revert "Bluetooth: btusb: fix QCA Rome suspend/resume"

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Date:   Tue, 2 Jan 2018 18:06:30 +0800
From:   Kai Heng Feng <kai.heng.feng@...onical.com>
To:     Daniel Drake <drake@...lessm.com>
Cc:     Brian Norris <briannorris@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Linux USB Mailing List <linux-usb@...r.kernel.org>,
        Linux Bluetooth mailing list 
        <linux-bluetooth@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Leif Liddy <leif.linux@...il.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH 1/2] Revert "Bluetooth: btusb: fix QCA Rome
 suspend/resume"



> On 21 Dec 2017, at 7:43 PM, Daniel Drake <drake@...lessm.com> wrote:
> 
> On Wed, Dec 20, 2017 at 6:53 PM, Brian Norris <briannorris@...omium.org> wrote:
>> 
>> On Wed, Dec 20, 2017 at 07:00:07PM +0800, Kai-Heng Feng wrote:
>>> This commit causes a regression on some QCA ROME chips. The USB device
>>> reset happens in btusb_open(), hence firmware loading gets interrupted.
>> 
>> Oh, did you really confirm that's the root of the problem? I was only
>> hypothesizing, with some informed observation and code review; but I
>> didn't fully convince myself. If so, that's interesting.
> 
> I have the same doubt. Can you explain how/why firmware uploading and
> btusb_open() overlap, and how this is avoided with your patch?

QCA ROME chip uploads its firmware inside btusb_open().

The behavior is like below:
- btusb_probe()
- btusb_open()
- btusb_suspend(), reset_resume gets set.
- btusb_open() again, hub resets the device, then the issue happens.

I didn’t dig really deep for the issue, I simply tried usb core quirks, it reset
the USB device before btusb_probe().

It might be that using the USB quirk only papers over the real issue.

> If they do overlap, is that not a bug in the stack that should be fixed instead?
> If the fix belongs in btusb and this BTUSB_RESET_RESUME thing really
> is problematic, should it be totally removed instead?

I think so. That’s why I need some insight from the original patch author.

Kai-Heng

> 
> Daniel