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

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Date:	Tue, 5 May 2015 20:22:49 +0000
From:	Jose Rivera <German.Rivera@...escale.com>
To:	Scott Wood <scottwood@...escale.com>,
	Dan Carpenter <dan.carpenter@...cle.com>
CC:	"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



> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, May 05, 2015 2:57 PM
> To: Dan Carpenter
> Cc: Rivera Jose-B46482; devel@...verdev.osuosl.org; Yoder Stuart-B08248;
> Hamciuc Bogdan-BHAMCIU1; arnd@...db.de; Sharma Bhupesh-B45370;
> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; agraf@...e.de;
> Erez Nir-RM30794; katz Itai-RM05202; Marginean Alexandru-R89243; Schmitt
> Richard-B43082
> 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?
> 
mc_bus->resource_pools[FSL_MC_POOL_IRQ].max_count is of type int16_t
(and is so, because its value comes from an MC API that returns
an int16_t). The reason for checking irq_count against 0x7ffff is to 
catch the case in which irq_count is out of range (irq_count originates
from values coming from the MC device, so we should do some validation
before using it)

Thanks,

German


> -Scott
>