4.10-rc3 rpi issues

[Michael Zoran]

On Wed, 2017-01-11 at 23:22 +0100, Stefan Wahren wrote:
> Hi Michael,
> 
> > Michael Zoran <mzoran at crowfest.net> hat am 11. Januar 2017 um 22:38
> > geschrieben:
> > 
> > 
> > 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
> > > >
> > 
> > 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.
> 
> This isn't a surprise. A new driver for a platform which is already
> supported by a mainline driver won't be accepted. Maybe the dwc2
> driver would have a better quality for bcm2835 if the Foundation
> would use it instead of the separate downstream driver. Instead of
> adding new driver it would be better to fix the existing one.

The two drivers have a different architecture.  The upstream driver
submits all the I/O to the hardware at once and relies on the hardware
sorting it out.  When the fixed number of slots are used, it just
breaks.

The downstream driver attempts to schedule the I/O in software and
submit it to the hardware piecemeal.   

I can understand the foundation's point of view on this.  The
"customer"/"Person paying for the device", doesn't care why USB isn't
working.  They don't care about the internal politics of the Linux
kernel source code.  They just know that they plugged in a few devices
and things broke.