linux-kernel - Re: [PATCH 5/8] ARM: zynq: add COMMON

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Message-ID: <20121102152826.GQ5190@beefymiracle.amer.corp.natinst.com>
Date:	Fri, 2 Nov 2012 09:28:26 -0600
From:	Josh Cartwright <josh.cartwright@...com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Mike Turquette <mturquette@...com>,
	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Linn <John.Linn@...inx.com>,
	Michal Simek <michal.simek@...inx.com>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
	Michal Simek <monstr@...str.eu>
Subject: Re: [PATCH 5/8] ARM: zynq: add COMMON_CLK support

On Fri, Nov 02, 2012 at 04:12:21PM +0100, Lars-Peter Clausen wrote:
> On 11/02/2012 02:38 PM, Josh Cartwright wrote:
> > On Fri, Nov 02, 2012 at 10:33:44AM +0100, Lars-Peter Clausen wrote:
> >> On 10/31/2012 07:58 PM, Josh Cartwright wrote:
[...]
> >>> +static void __init zynq_periph_clk_setup(struct device_node *np)
> >>> +{
> >>> +	struct zynq_periph_clk *periph;
> >>> +	const char *parent_names[3];
> >>> +	struct clk_init_data init;
> >>> +	struct clk *clk;
> >>> +	int err;
> >>> +	u32 reg;
> >>> +	int i;
> >>> +
> >>> +	err = of_property_read_u32(np, "reg", &reg);
> >>> +	WARN_ON(err);
> >>
> >> Shouldn't the function abort if a error happens somewhere? Continuing here
> >> will lead to undefined behavior. Same is probably true for the other WARN_ONs.
> >
> > The way I see it is: the kernel is will be left in a bad state in the
> > case of any failure, regardless of if we bail out or continue.  AFAICT,
> > there is no clean way to recover from a failure this early.
> >
> > Given that, it seems simpler (albeit marginally so) just to continue; so
> > that's what I chose to do.  I'm not opposed to bailing out, just not
> > convinced it does anything for us.
> >
> The issue with this approach is that, while you get a warning, unexpected
> seemingly unrelated side-effects may happen later on. E.g. if no reg
> property for the clock is specified the reg variable will be uninitialized
> and contain whatever was on the stack before. The clock will be registered
> nonetheless and the boot process continues. Now if the clock is enabled a
> bit in a random register will be modified, which could result in strange and
> abnormal behavior, which can be very hard to track down.

Okay.....but any reasonable person would start their debugging quest at
the source of the WARN_ON.  If someone sees the WARN_ON message but
stupidly chooses to ignore it, they deserves to spend the time trying to
track down abnormal behavior, so I'm still not convinced.

  Josh

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