[PATCH] drm/xe: Fix coverity issue, truncation warning

[Jani Nikula]

On Tue, 05 Aug 2025, "Gurram, Pravalika" <pravalika.gurram at intel.com> wrote:
>> -----Original Message-----
>> From: Brost, Matthew <matthew.brost at intel.com>
>> Sent: Tuesday, August 5, 2025 9:05 AM
>> To: Gurram, Pravalika <pravalika.gurram at intel.com>
>> Cc: intel-xe at lists.freedesktop.org; Wajdeczko, Michal
>> <Michal.Wajdeczko at intel.com>
>> Subject: Re: [PATCH] drm/xe: Fix coverity issue, truncation warning
>> 
>> On Mon, Aug 04, 2025 at 04:14:09PM +0530, Pravalika Gurram wrote:
>> > Use conditional assignment to avoid cast truncation warning.
>> > Set instance to 0 when hw_reports_to_instance_zero() returns false.
>> >
>> > Fixes: 95336cfd5b2ce ("drm/xe: Add memirq report page address
>> > helpers")
>> 
>> Definitiely no fixes tag required here.
>> 
>> >
>> > Signed-off-by: Pravalika Gurram <pravalika.gurram at intel.com>
>> > ---
>> >  drivers/gpu/drm/xe/xe_memirq.c | 3 ++-
>> >  1 file changed, 2 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/gpu/drm/xe/xe_memirq.c
>> > b/drivers/gpu/drm/xe/xe_memirq.c index 49c45ec3e83c..75ddf4eda355
>> > 100644
>> > --- a/drivers/gpu/drm/xe/xe_memirq.c
>> > +++ b/drivers/gpu/drm/xe/xe_memirq.c
>> > @@ -257,7 +257,8 @@ static u32 __memirq_source_page(struct xe_memirq
>> *memirq, u16 instance)
>> >  	memirq_assert(memirq, instance <= XE_HW_ENGINE_MAX_INSTANCE);
>> >  	memirq_assert(memirq, memirq->bo);
>> >
>> > -	instance = hw_reports_to_instance_zero(memirq) ? instance : 0;
>> > +	if (!hw_reports_to_instance_zero(memirq))
>> > +		instance = 0;
>> 
>> I'm failing to see how this fixes any possible static checker. Could you explain?
>> 
>> That said, I do prefer the way you have changed it here.
>> 
>> Matt
>> 
>> 
> The Static analyzer treating the ternary expression "hw_reports_to_instance_zero(memirq) ? instance : 0" evaluates to a 32-bit value
> Hence, I have added if condition to avoid a static checker error
> cast overflow: Truncation due to cast operation on hw_reports_to_instance_zero(memirq) ? instance : 0 from 32 to 16 bits.

Obviously it's not possible for this expression to truncate anything,
and the static analyzer is being silly.

BR,
Jani.


>
> Pravalika
>
>> >  	return xe_bo_ggtt_addr(memirq->bo) +
>> > XE_MEMIRQ_SOURCE_OFFSET(instance);
>> >  }
>> >
>> > --
>> > 2.34.1
>> >

-- 
Jani Nikula, Intel