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

Eric Anholt eric at anholt.net
Mon Mar 20 10:22:42 PDT 2017

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.
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