[PATCH] ARM: multi_v7_defconfig: major refresh

[tixy@linaro.org (Jon Medhurst (Tixy))]

On Fri, 2014-08-01 at 12:12 +0100, Sudeep Holla wrote:
> 
> On 01/08/14 12:03, Olof Johansson wrote:
> > On Fri, Aug 1, 2014 at 4:01 AM, Jon Medhurst (Tixy) <tixy@linaro.org> wrote:
> >> On Fri, 2014-08-01 at 11:26 +0100, Sudeep Holla wrote:
> >>>
> >>> On 22/07/14 19:01, Olof Johansson wrote:
> >>>> This is a major refresh of the multi_v7_defconfig:
> >>>>
> >>>> - Bring over a bunch of Samsung drivers to make ODROID-U3 and Chromebooks usable
> >>>>    * Enable big.LITTLE
> >>>>    * MCPM
> >>> [...]
> >>
> >>>> +CONFIG_BIG_LITTLE=y
> >>>> +CONFIG_BL_SWITCHER=y
> >>>
> >>> IIUC, this will enable switcher code by default. I am not sure if this
> >>> is intentional ? E.g.: After this I can have only 2 active cpus instead
> >>> of 5 on my Vexpress TC2 platform.
> >>>
> >>> IMO we can keep this enabled by default in the build, but disabled
> >>> by default on boot.
> >>
> >> TC2 has a big.LITTLE processor and the switcher is the only mainlined
> >> way of making any kind of proper use of big.LITTLE, so why not have it
> >> enabled by default?
> >
> > +1.
> >
> >>
> >>>   One way to achieve this:
> >>> (There's sysfs to re-enable it runtime)
> >>
> >> The opposite is also true, if you don't want the switcher enabled you
> >> can disable it by the same method after boot ;-)
> >>
> >>> -->8
> >>> diff --git a/arch/arm/common/bL_switcher.c b/arch/arm/common/bL_switcher.c
> >>> index 490f3dced749..f4c36e70166a 100644
> >>> --- a/arch/arm/common/bL_switcher.c
> >>> +++ b/arch/arm/common/bL_switcher.c
> >>> @@ -794,7 +794,7 @@ static int bL_switcher_hotplug_callback(struct
> >>> notifier_block *nfb,
> >>>           return NOTIFY_DONE;
> >>>    }
> >>>
> >>> -static bool no_bL_switcher;
> >>> +static bool no_bL_switcher = true;
> >>
> >> This changes the default for everyone, which I guess is fair enough if
> >> there is a good reason, but I'm not sure there is.
> >
> > No, I don't think there is.
> >
> 
> It's just that people using TC2 will suddenly see 3 of the 5 CPUs missing.

Yes, if they we're previously using multi_v7_defconfig (do people
working specifically with TC2's use that?)

Conversely, with the change in default proposed above, anyone with their
own configs enabling the switcher will suddenly see the number of CPUs
go from 2 to 5. We also have the situation where we have a config
option, which when enabled, doesn't actually do anything unless the user
also changes boot arguments or takes measures to enable it after boot.
Which seems the wrong way for things to work to me.

I believe that if we don't want the switcher enabled in kernels built
with multi_v7_defconfig, then it should be done by not adding the config
option to multi_v7_defconfig in the first place.

-- 
Tixy