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Subject: Re: [Intel-gfx] include/drm/i915_drm.h:96: possible bad bitmask ?
To: Dave Airlie <airlied@gmail.com>,
        David Binderman <linuxdev.baldrick@gmail.com>,
        "Vetter, Daniel" <daniel.vetter@intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        David Airlie <airlied@linux.ie>, dcb314@hotmail.com,
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From: Dave Gordon <david.s.gordon@intel.com>
Organization: Intel Corporation (UK) Ltd. - Co. Reg. #1134945 - Pipers Way,
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Date: Tue, 9 Aug 2016 17:01:15 +0100
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On 09/08/16 03:59, Dave Airlie wrote:
> On 8 August 2016 at 19:40, Daniel Vetter <daniel@ffwll.ch> wrote:
>> On Mon, Aug 08, 2016 at 10:31:32AM +0100, David Binderman wrote:
>>> Hello there,
>>>
>>> Recent versions of gcc say this:
>>>
>>> include/drm/i915_drm.h:96:34: warning: result of ‘65535 << 20’
>>> requires 37 bits to represent, but ‘int’ only has 32 bits
>>> [-Wshift-overflow=]
>>>
>>> Source code is
>>>
>>> #define   INTEL_BSM_MASK (0xFFFF << 20)
>>>
>>> Maybe something like
>>>
>>> #define   INTEL_BSM_MASK (0xFFFFUL<< 20)
>>>
>>> might be better.
>>
>> Yup. Care to bake this into a patch (with s-o-b and everything per
>> Documentation/SubmittingPatches) so I can apply it?
>
> Why would you want to apply a clearly incorrect patch :-)
>
> INTEL_BSM_MASK is used in one place, on a 32-bit number
>
> I'm not sure what it needs to be, but a 64-bit number it doesn't.
>
> Dave.

I found two uses, but in both cases it's masking a value read
from a 32-bit PCI register, so it can just be (-(1 << 20)).

.Dave.