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

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Date:	Mon, 5 Nov 2012 13:31:59 +0100
From:	Michal Simek <michal.simek@...inx.com>
To:	Josh Cartwright <josh.cartwright@...com>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	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>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 5/8] ARM: zynq: add COMMON_CLK support

2012/11/2 Josh Cartwright <josh.cartwright@...com>:
> 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.

I am with Lars. You would be surprised how many people do no read bootlog.
It should be handled better.

Thanks,
Michal
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