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

[Liviu.Dudau@arm.com (Liviu Dudau)]

On Sat, Mar 07, 2015 at 10:24:08PM +0000, Linus Walleij wrote:
> On Fri, Feb 27, 2015 at 3:06 PM, Liviu Dudau <Liviu.Dudau@arm.com> wrote:
> > On Fri, Feb 27, 2015 at 01:07:42PM +0000, Linus Walleij wrote:
> 
> >> 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).
Linus, 

> 
> OK now I feel bad and maybe I was not in such a good mood that day.

Don't worry, I actually found it amusing.

> 
> The LEDs I added are really useful on the other ARM reference designs,
> the heartbeat gives a sign that the system is alive even if your console is
> not working and that's what I appreaciate a lot about it (the
> heartbeat intensity
> also indicates system load).
> 
> The MMC read/write LED is as useful as the hard disk activity LED on
> some older PCs, kinda nice if you want to know something is going on.
> 
> The rest of the LEDs show which CPU cores are active. This was the
> original use of the LEDs on the RealView PB11MPcore and it was
> appreciated by the multicore developers who could see the different
> CPUs being busy with tasks.

In that case you might want to use the remaining 2 leds for cpus 4 and 5,
as Juno has a total of 6 cores. Your current patch leaves two LEDs unassigned.

> 
> LEDs on development boards are real nice, simply, and I think also
> some deployed ARM64 server systems will have them.

Agree on LEDs being nice. I'm guessing that on server side if you want blinking lights
you need ACPI? ;)

Best regards,
Liviu

> 
> Yours,
> Linus Walleij
> 

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