linux-kernel - Re: [PATCH 2/3] drm/i915: split out check for noncontiguous pfn range

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Message-ID: <20170321095652.GB11338@nuc-i3427.alporthouse.com>
Date:   Tue, 21 Mar 2017 09:56:52 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] drm/i915: split out check for noncontiguous pfn range

On Mon, Mar 20, 2017 at 10:40:28AM +0100, Arnd Bergmann wrote:
> We get a warning with gcc-7 about a pointless comparison when
> using a linear memmap:
> 
> drivers/gpu/drm/i915/selftests/scatterlist.c: In function 'alloc_table':
> drivers/gpu/drm/i915/selftests/scatterlist.c:219:66: error: self-comparison always evaluates to false [-Werror=tautological-compare]
> 
> Splitting out the comparison into a separate function avoids the warning
> and makes it slightly more obvious what happens.

I worried whether gcc will simply get smarter and apply its warning more
consistently, but I agree the helper is good documentation.
 
> Fixes: 935a2f776aa5 ("drm/i915: Add some selftests for sg_table manipulation")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre