linux-kernel - Re: [PATCH 1/7] staging: fsl-mc: MC bus IRQ support

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Date:	Tue, 5 May 2015 14:56:41 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	Jose Rivera <German.Rivera@...escale.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Stuart Yoder <stuart.yoder@...escale.com>,
	"bhamciu1@...escale.com" <bhamciu1@...escale.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"bhupesh.sharma@...escale.com" <bhupesh.sharma@...escale.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"agraf@...e.de" <agraf@...e.de>,
	"nir.erez@...escale.com" <nir.erez@...escale.com>,
	"itai.katz@...escale.com" <itai.katz@...escale.com>,
	"R89243@...escale.com" <R89243@...escale.com>,
	Richard Schmitt <richard.schmitt@...escale.com>
Subject: Re: [PATCH 1/7] staging: fsl-mc: MC bus IRQ support

On Tue, 2015-05-05 at 19:40 +0300, Dan Carpenter wrote:
> On Tue, May 05, 2015 at 04:08:49PM +0000, Jose Rivera wrote:
> > > Subject: Re: [PATCH 1/7] staging: fsl-mc: MC bus IRQ support
> > > 
> > > On Mon, May 04, 2015 at 10:09:08PM +0000, Jose Rivera wrote:
> > > > > > +		WARN_ON((int16_t)irq_count < 0);
> > > > >
> > > > > This code is doing "WARN_ON(test_bit(15, (unsigned long
> > > *)&irq_count));".
> > > > > That seems like nonsense.  Anyway, just delete the WARN_ON().
> > > > >
> > > > I disagree. This WARN_ON is checking that irq_count is in the expected
> > > > range (it fits in int16_t as a positive number). The
> > > > dprc_scan_objects() function expects irq_count to be of type "unsigned
> > > > int" (which is 32-bit unsigned)
> > > >
> > > 
> > > You're not allowed to disagree because it's a testable thing and not an
> > > opinion about style or something.  :P  What you want is:
> > > 
> > > 	WARN_ON(irq_count > SHRT_MAX);
> > > 
> > I see your point now. The check "(int16_t)irq_count < 0)" will not be able
> > to catch 0x10000 > 0x7fff, but "irq_count > SHRT_MAX) will. So I'll
> > make the suggested change, but I would prefer to use S16_MAX rather than 
> > SHRT_MAX.
> > 
> 
> Huh?  I didn't even know about the S16_MAX definition.  There are
> literally no users of it in the kernel.  It's not very fair because
> there are few users of SHRT_MAX.  But there are literally no users of
> S32_MAX in the kernel and 358 users of INT_MAX.
> 
> Don't insist that you must be special and different from everyone else.

There are some users of U16_MAX, U32_MAX, and U64_MAX.  Why use a limit
for a different type than is being used?  Why have s16/s32 at all if
you're going to conflate it with short/int elsewhere?

That said, I don't see where this code is actually using s16 (or
int16_t) for irq_count except in these weird error checks.  German, why
do you need to check against 0x7fff (whatever you call it) at all?
Won't comparing to a promoted-to-unsigned-int .max_count (as you do
immediately after the WARN_ON) suffice?

-Scott


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