linux-kernel - Re: [PATCH] PM / OPP: fix debugfs files for 64-bit

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Message-ID: <5308760.2G5KJFF9Pi@wuerfel>
Date:	Wed, 07 Oct 2015 21:12:55 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Nishanth Menon <nm@...com>,
	Dmitry Torokhov <dtor@...omium.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] PM / OPP: fix debugfs files for 64-bit

On Wednesday 07 October 2015 18:33:24 Viresh Kumar wrote:
> Cc'ing Mike and Stephen..
> 
> On 07-10-15, 13:57, Greg Kroah-Hartman wrote:
> > On Wed, Oct 07, 2015 at 04:51:49PM +0530, Viresh Kumar wrote:
> > > On 07-10-15, 12:07, Greg Kroah-Hartman wrote:
> > > > Why would you be wanting to create a "unsigned long" as an api anyway?
> > > > Just force it to be u64 all the time, can't you do that?
> > > 
> > > Okay, so the variable in question (lets say frequency) is an 'unsigned
> > > long' and that's how all the APIs of clock framework expect/define
> > > it.
> > > 
> > > And you are probably saying that we do this:
> > > 
> > > unsigned long freq;
> > > 
> > > debugfs_create_u64((u64 *)&freq);
> > > 
> > > Right? Or are you asking to update clock APIs to be converted to u64?
> > 
> > Yes, they should be u64 as I doubt you want to debug problems that you
> > have in the driver where it works on a 64bit system but doesn't on a
> > 32bit one.
> 
> Firstly changing the clock API (and other similar APIs) to make
> frequency u64 instead of 'unsigned long', looks like a giant effort.
> There are too many users of those API, etc..
> 
> Over that, it might be good performance wise to use u32 for 32 bit
> systems and u64 for 64 bit one, to represent clock frequency and maybe
> that's why we chose unsigned long there.

I think it clearly makes sense to have a fixed length for each of these
members: either 32 bit is enough to represent all possible values, then
there is no need to make them 'long' on 64-bit architectures, or 32 bit
is not enough and then the code is broken on 32-bit architectures today
and should be fixed.

In my patch, I assumed that if 32-bit architectures work fine today, then
we don't need more range on 64-bit architectures either.

	Arnd
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