4.10-rc3 rpi issues

[Michael Zoran]

On Fri, 2017-01-13 at 22:39 +0100, Stefan Wahren wrote:
> Hi Michael,
> 
> > Michael Zoran <mzoran at crowfest.net> hat am 13. Januar 2017 um 21:59
> > geschrieben:
> > 
> > 
> > On Fri, 2017-01-13 at 21:44 +0100, Stefan Wahren wrote:
> > > Hi Michael,
> > > 
> > > > Michael Zoran <mzoran at crowfest.net> hat am 12. Januar 2017 um
> > > > 01:26
> > > > geschrieben:
> > > > 
> > > > 
> > > > 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 re
> > > > > > > dhat
> > > > > > > .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.
> > > 
> > > do you mean the microframe scheduler which is also available in
> > > dwc2
> > > but disabled for bcm2835?
> > 
> > Very interesting... I didn't know about that feature. Is it
> > disabled on
> > bcm2835 because some hardware functionality was intentionally
> > disabled
> > for marketing reasons?
> 
> i don't know why. But this feature was buggy. 
> 
> But Douglas Anderson rewrote this feature last year [1]. Maybe we
> should give it try now?

Sure.  I'll see if I can enable it on a local build and do some
testing.   Thanks for letting me know about this.