DVB USB firmware download problems

DVB USB firmware download problems

suspend / resume

I listed fixing resume from the suspend as a one topic of the DVB USB to fix. There has been very long time nasty suspend / resume bugs which seems to be related for the firmware downloading. Reason has not been clear thus those were never fixed. I found one bug report back from the 2009 which was sent for me, as my af9015 driver crashes during resume. At that time I didn't have much experience how to hunt bug like that, which was out of my chip driver. I made simplest possible DVB USB driver which just requests firmware download - and crashes - just as a proof of concept. Unfortunately I did not get any help and it left unresolved.
Crash I made 2009: DVB USB resume from suspend crash

Fedora 17 installation to the SSD

As I got very many Kernel crashes during the development and every crash means booting which wastes time around 10 minutes per boot. Also Fedora 17 was just released and I wanted to install it, so I decided to buy new SSD and install Fedora 17! Install goes nicely, taking only minute or two, it is unbelievable how fast SSD is. I have to say hate Gnome3 UI, thus I was earlier running it "fallback" mode but now I decided to give opportunity for Cinnamon.

DVB USB devices on Fedora 17

Finally I started to test how DVB devices were working. It came as a small surprise that plugging DVB USB stick in hangs device around 30 seconds until it appeared. Looked the logs and there was udev errors. It was not totally broken as it still started working but takes 30 seconds and it happened for every DVB USB device which uses firmware.


Jun  1 19:24:24 localhost kernel: [   59.820552] dvb-usb: found a 'Afatech AF9015 DVB-T USB2.0 stick' in cold state, will try to load a firmware
Jun  1 19:24:54 localhost udevd[423]: worker [1581] timeout, kill it
Jun  1 19:24:54 localhost kernel: [   89.853168] dvb-usb: downloading firmware from file 'dvb-usb-af9015.fw'

udev and blocking firmware download at module_init()

Clear suspicion was udev as there was nothing changed inside DVB USB which could break it like that. I downgraded udev to Fedora 16 version and it started working. As I was not any familiar with the udev I decided to open ticket for the Fedora Bugzilla targeting it udev. It didn't take many minutes Kay Sievers replied to Bugzilla, explaining it is Kernel driver issue as it blocks module_init() by downloading firmware. The reason it now arises is udev. Its behavior was changed and we wasn't aware that it was needed to change Kernel drivers not to block module_init().
Fedora Bugzilla: DVB USB device firmware requested in module_init()

The fix

I implemented non-blocking module_init() / USB probe() for DVB USB and problem disappeared. It was done by delaying old probe functionality, which downloads firmware too, using Kernel workqueue and returning always success for the probe() / module_init(). Doing it that way is not prettiest option at least for my mind but there is no any better I am aware. Downside here is that we must deregister device in case of something fails during "old probe". I did that de-registering using usb_driver_release_interface().

suspend / resume fixed too?

I was unable to reproduce old, and very well known, suspend / resume bug with my current hardware and software. Anyhow, it is quite likely coming from the same blocking firmware download issue. Resume from the suspend behaves quite similarly as plugging DVB USB stick to the USB port.

There is still another existing suspend bug. If you are streaming DVB device, like watching television, it will never go to the sleep. It just hangs. That is DVB core issue as in my understanding there should be some mechanism to stop stream before going to sleep. I will fix that later this sumer after DVB USB issues are fixed.