Re: [PATCH v6 2/2] ARM hibernation / suspend-to-disk

From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Sebastian Capella <sebastian.capella@linaro.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"linaro-kernel@lists.linaro.org" <linaro-kernel@lists.linaro.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	Russ Dill <Russ.Dill@ti.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Russell King <linux@arm.linux.org.uk>,
	Len Brown <len.brown@intel.com>, Nicolas Pitre <nico@linaro.org>,
	Santosh Shilimkar <santosh.shilimkar@ti.com>,
	Will Deacon <Will.Deacon@arm.com>,
	Jonathan Austin <Jonathan.Austin@arm.com>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>,
	Stephen Boyd <sboyd@codeaurora.org>
Subject: Re: [PATCH v6 2/2] ARM hibernation / suspend-to-disk
Date: Tue, 4 Mar 2014 11:17:46 +0000	[thread overview]
Message-ID: <20140304111745.GB21431@e102568-lin.cambridge.arm.com> (raw)
In-Reply-To: <5315a319.a3b2440a.039b.ffffc66e@mx.google.com>

On Tue, Mar 04, 2014 at 09:55:31AM +0000, Sebastian Capella wrote:
> Quoting Sebastian Capella (2014-02-28 15:38:54)
> > Quoting Lorenzo Pieralisi (2014-02-28 14:49:33)
> > > On Fri, Feb 28, 2014 at 08:15:57PM +0000, Sebastian Capella wrote:
> > > > > 
> > > > > This does not guarantee your stack is 8-byte aligned, that's not AAPCS
> > > > > compliant and might buy you trouble.
> > > > > 
> > > > > Either you align the stack or you align the pointer you are passing.
> > > > > 
> > > > > Please have a look at kernel/process.c
> > > > 
> > > > I've added this for now, do you see any issues?
> > > > 
> > > > -static u8 resume_stack[PAGE_SIZE/2] __nosavedata;
> > > > +static u64 resume_stack[PAGE_SIZE/2/sizeof(u64)] __nosavedata;
> > > > -               resume_stack + sizeof(resume_stack));
> > > > +               resume_stack + ARRAY_SIZE(resume_stack));
> > > 
> > > I do not see why the stack depends on the PAGE_SIZE. I would be surprised
> > > if you need more than a few bytes (given that soft_restart switches stack
> > > again...), go through it with a debugger, it is easy to check the stack
> > > usage and allow for some extra buffer (but half a page is not needed).
> > 
> > I assuming this is becase the no-save region is one page anyway (we skip
> > restoring the no-save region physical page).  So maybe 1/2 is a way to
> > leave some room for whatever else may need to be here, but in any case
> > the 4k is used for nosave.  I think you're right that it can be much less.
> 
> Hi Lorenzo,
> 
> Are you ok with this just being half a page?  Or do you want me to try
> to reduce the stack size?  I am at Connect without my debugger, so in
> that case it would have to wait until next week.

I am ok, either you leave that as it is (that multiple division looks
horrible but it is just nitpicking on my side) or define it as an u8 array,
stick __attribute__((aligned(8)) to the definition (and explain why) and be
done with it.

You can add my:

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>