[PATCH 1/6] bcm2835-gpio-exp: Driver for GPIO expander via mailbox service

[Michael Zoran]

On Mon, 2017-03-20 at 10:22 -0700, Eric Anholt wrote:
> Michael Zoran <mzoran at crowfest.net> writes:
> 
> > > > Since the API is completely documented, I see no reason we or
> > > > anybody
> > > > couldn't essentially rewrite the driver while it's in
> > > > staging.  I
> > > > just
> > > > think it would be best for everyone if the new version was a
> > > > drop
> > > > in
> > > > replacement for the original version.  Essential an enhancement
> > > > rather
> > > > then a competitor.
> > > 
> > > I think my comments weren't fundamental changes, but you surely
> > > mean
> > > the devicetree ABI? I like to see this driver ASAP out of staging
> > > and
> > > i'm not interested to maintain 2 functional identical driver only
> > > to
> > > keep compability with the Foundation tree. Currently i'm afraid
> > > that
> > > we build up many drivers in staging, which need a complete
> > > rewrite
> > > later if they should come out of staging. It would be nice if we
> > > could avoid the situation we have with the thermal driver.
> > > 
> > > Stefan
> > 
> > The API I'm talking about here is the mailbox API that is used to
> > talk
> > to the firmware.  The numbers and structures to pass are
> > documented. 
> > Nothing prevents anybody from rewriting this driver and submitting
> > it
> > to the appropriate subsystems.  It's certainly small enough.
> > 
> > If you really want working thermal or cpu speed drivers today,
> > nothing
> > stops anybody from submitting the downstream drivers after doing
> > some
> > minor touchups and submitting them to staging.  That would at least
> > get
> > things working while people argue about what the correct DT nodes
> > should be.
> > 
> > I would also like to point out that the RPI 3 has been out for over
> > a
> > year and nobody has been able to get working video out of it
> > through
> > VC4 on a mainline tree.  At least until now.  So I'm not sure the
> > best
> > way to go is for the expander driver to go under the GPIO subtree.
> 
> Excuse me?  Display works fine on my Pi3.  VC4 uses DDC to probe for
> connection when the GPIO line isn't present in the DT.

Is this arm32 or arm64 modes? And is this through the simplefb that was
adding for testing is the VC4 driver fully driving the display.  Is VC4
still in the .config that you used? Is this a standard version of VC4,
or does it include modifications for testing purposes?

If it works so well as is, why do you need or want the expander?  You
tried to submit a very similar version a year ago?