[PATCH 1/2] arm64: juno: Add APB registers and LEDs using syscon

[Liviu Dudau]

On Fri, Feb 27, 2015 at 01:07:42PM +0000, Linus Walleij wrote:
> On Wed, Feb 25, 2015 at 4:11 PM, Liviu Dudau <Liviu.Dudau at arm.com> wrote:
> > On Wed, Feb 25, 2015 at 03:00:23PM +0000, Will Deacon wrote:
> >> On Wed, Feb 25, 2015 at 02:47:56PM +0000, Liviu Dudau wrote:
> >> > On Wed, Feb 25, 2015 at 01:55:12PM +0000, Will Deacon wrote:
> >> > > On Wed, Feb 25, 2015 at 12:16:29PM +0000, Linus Walleij wrote:
> >> > > > This defines the Juno "APB system registers" as a syscon device,
> >> > > > and all the LEDs controlled by the APB system registers right
> >> > > > below it using the syscon LEDs driver on top of syscon. Define
> >> > > > LED0 for heartbeat, LED1 for MMC0 activity and the following
> >> > > > four LEDs indicating CPU activity using the Linux-specific
> >> > > > DT bindings for triggers.
> >> > > >
> >> > > > This is the pattern and same drivers as used on the legacy
> >> > > > platform device trees for the ARM Integrators and the RealView
> >> > > > PB1176.
> >> > >
> >> > > Stupid question, but where are these LEDs located on the platform? I tried
> >> > > enabling this, but all it seemed to do was make hackbench slightly slower :)
> >> >
> >> > http://infocenter.arm.com/help/topic/com.arm.doc.ddi0524c/deb1353593789871.html
> >> >
> >> > Section 1.3, look at the left hand side, above the user push buttons.
> >>
> >> Right, so these LEDs are *inside* the case. Is that really something worth
> >> enabling for defconfig?
> >
> > Depends on the case :) You might have a nice cutout in the plastic of the VExpress
> > box, or have your own custom acrylic box.
> 
> Of course I take off the lid, who doesn't want to see the nice electronics.
> This is analogous to using some other naked ARM reference design
> like the Versatile or the RealView PB1176 where you can just put your
> fingers on the board if you like.
> 
> > Maybe Linus can explain to us why he thinks this functionality is useful given
> > that quite a lot of people tend to use the Juno boards inside the original boxes
> > for fear of ESD accidents.
> 
> Wut? Ask the guy who designed the box.
> 
> Notice that the SD card slot is *ALSO* inside the box, do you mean we
> should then also delete the uSD card support added in
> commit 71f867ec130e3cc8e692366fdf8941ded27c727e
> by yourself because the SD card slot is not reachable?
> Notice that to access that card slot you even have to remove the
> nice blue ARM boilerplate.

That's not my view. I have a mobile phone with an uSD card slot, but I have to take
the cover off (and the battery) to access it. It doesn't mean I should not be able
to use it from kernel side because of that, only that the designer of the phone
(and of the Juno board + box by extension) did not expect people to use it with
covers off all the time.


<virtual-tongue-in-cheek-on>
I fail to see why you need to remove the SD card all the time. Surely opening
the case once to put the uSD card in is enough? ;)
</virtual-tongue-in-cheek-on>

> 
> The board is obviously designed to be reachable and the top part
> of the case is obviously designed to be taken off by professional
> users.

I'm mostly on your side, Linus, I was just looking for more use cases. Like I've said,
most of our customers seem to keep the case closed (or at least that is what they tell
us :) ) so I'm looking for explanations on how you use the LEDs (visual debugging for
big-LITTLE was how Lorenzo was using them on TC2 for example).

Best regards,
Liviu

> 
> Yours,
> Linus Walleij
> 

-- 
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