Re: [PATCH v2 1/6] drm/i915/gem: fix bitwise and logical AND mixup

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 26 Sep 2024, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> On Wed, Sep 18, 2024 at 08:35:43PM +0300, Jani Nikula wrote:
>> CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND is an int, defaulting to 250. When
>> the wakeref is non-zero, it's either -1 or a dynamically allocated
>> pointer, depending on CONFIG_DRM_I915_DEBUG_RUNTIME_PM. It's likely that
>> the code works by coincidence with the bitwise AND, but with
>> CONFIG_DRM_I915_DEBUG_RUNTIME_PM=y, there's the off chance that the
>> condition evaluates to false, and intel_wakeref_auto() doesn't get
>> called. Switch to the intended logical AND.
>> 
>> v2: Use != to avoid clang -Wconstant-logical-operand (Nathan)
>
> oh, this is ugly!
>
> Wouldn't it be better then to use IS_ENABLED() macro?

It's an int config option, not a bool. (Yes, the name is misleading.)

IS_ENABLED(CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND) would be the same as
CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND == 1.

We're actually checking if the int value != 0, so IMO the patch at hand
is fine.

BR,
Jani.


>
>> 
>> Fixes: ad74457a6b5a ("drm/i915/dgfx: Release mmap on rpm suspend")
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> Cc: Anshuman Gupta <anshuman.gupta@intel.com>
>> Cc: Andi Shyti <andi.shyti@linux.intel.com>
>> Cc: Nathan Chancellor <nathan@kernel.org>
>> Cc: <stable@vger.kernel.org> # v6.1+
>> Reviewed-by: Matthew Auld <matthew.auld@intel.com> # v1
>> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> # v1
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>> index 5c72462d1f57..b22e2019768f 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>> @@ -1131,7 +1131,7 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
>>  		GEM_WARN_ON(!i915_ttm_cpu_maps_iomem(bo->resource));
>>  	}
>>  
>> -	if (wakeref & CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND)
>> +	if (wakeref && CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND != 0)
>>  		intel_wakeref_auto(&to_i915(obj->base.dev)->runtime_pm.userfault_wakeref,
>>  				   msecs_to_jiffies_timeout(CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND));
>>  
>> -- 
>> 2.39.2
>> 

-- 
Jani Nikula, Intel