4.10-rc3 rpi issues

[Michael Zoran]

On Wed, 2017-01-11 at 16:46 +0000, Peter Robinson wrote:
> On Wed, Jan 11, 2017 at 2:29 PM, Gerd Hoffmann <kraxel at redhat.com>
> wrote:
> >    Hi,
> > 
> > Moved my pile of patches forward to 4.10-rc3, so I can see what
> > actually
> > landed in the 4.10 merge window, and go try send/resend patches for
> > 4.11
> > 
> > Trapped into a bunch of problems:
> > 
> > usb is flaky.  raspberry pi 2 b.  Has a edimax wifi dongle, and
> > that
> > stopped working.  rtl8xxxu driver.  Doesn't find any wifi
> > networks.  usb
> > keyboard has problems too, looses keys now and then, which makes me
> > think this is more a usb than a wifi problem.  I had that before,
> > with
> > the 4.8 kernels.  4.9 works fine.  Now with 4.10-rc3 the problems
> > are
> > back :(  Anyone seen this too?  Any clues what this might be?
> > 
> > Non-modular kernel crashes at boot.  Using that to netboot kernels
> > cross-compiled on my faster x86 box.  Have no serial console hooked
> > up,
> > so no logs for now, sorry.  But maybe anyone has an idea
> > nevertheless?
> 
> The Fedora built rc3 kernel seems OK. I'm using usb wifi ATM without
> too many issues and haven't had any drop outs. I've seen some
> interesting bits with CMA which I reported [1]. USB doesn't appear at
> least in my testing to be any worse on the 2 or 3.

The upstream USB driver has many, many limitations.   I'm not surprised
that you're having intermittent issues.  The issues are worse if you
have many devices attached or you have devices of very different
speeds(say keyboard + Wifi).

I'm actually surprised that somebody hasn't tried to upstream the
downstream USB driver which has less limitations.  The DWC USB
controller is not Broadcom specific so it would apply to more then the
RPI.  I would be interested in helping with such an effort and it may
even be possibly to write the driver from "scratch".  The hardest part
would be getting something like a PI Zero that doesn't have the USB hub
soldered onto the board so that it's easy to attach a USB bus analyzer
for better debugging.

As for the non modular kernel, I've hit a similar issue with the VC4
driver.  I see the lockups/crashes when the kernel switches from
simplefb to VC4.  If video speed isn't important for your application,
one thing I've found that works myself is remove the VC4 driver from
the kernel build config.  That way the kernel will stay with simplefb. 
It is necessary to keep VC4 enabled in the device tree if you go that
path since the firmware will only enable simplefb if VC4 is detected in
the device tree.

Of course, VC4 works fine if you have modules enabled.