Re: [PATCH linux dev-4.7 v3 2/2] ARM: dts: Enable checkstop and cooling gpio keys

[Andrew Jeffery <andrew@aj.id.au>]

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On Wed, 2017-04-19 at 10:38 -0400, Brad Bishop wrote:
> > > > On Apr 19, 2017, at 10:29 AM, Andrew Jeffery <andrew@aj.id.au> wrote:
> > 
> > Hi Brad,
> > 
> > If you do future revisions of these patches, can you please Cc me?
> 
> will do.
> 
> > 
> > On Wed, 2017-04-19 at 00:18 -0400, Brad Bishop wrote:
> > > Enable gpio-keys events for the checkstop and water/air cooled
> > > gpios for use by applications on the Witherspoon system.
> > > 
> > > > Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
> > > 
> > > ---
> > >  arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts | 20 ++++++++++++++++++++
> > >  1 file changed, 20 insertions(+)
> > > 
> > > diff --git a/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts b/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> > > index e3a7b77..aa1708e 100644
> > > --- a/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> > > +++ b/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> > > @@ -31,6 +31,26 @@
> > > > > > > >  		};
> > > >  	};
> > > 
> > >  
> > > +	gpio-keys@0 {
> > 
> > does the @0 give us a stable device name for userspace to open?
> 
> No it doesn’t.  This is my lack of DT skillz showing.  I was looking
> into how we can give userspace a stable device name.  I was going
> down the udev path but I can’t find any any of the information from
> these DT nodes in the udev event.
> 
> > 
> > Do we really want to go this way? We now have useful unique codes for
> > the "key"s, why not use the one node? Or is your concern we've now tied
> 
> Each gpio will have an application waiting for its state to change.  My
> concern was waking up x number of applications every time any gpio changes
> state.  Is that a valid concern?

How many applications do we expect to be reading the evdev? What are
our expected interrupt rates? What are the worst expected cases?

It's hard to judge without knowing the numbers, but considering the
chips we run on I agree we should generally favour performance if
design is getting in the way. But to make that trade off we should be
clear on the performance numbers.

Andrew

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