Re: [PATCH] drm/i915/: Initialise trans_min for skl_compute_transition_wm()

Mahesh Kumar
2017-11-09T03:46:33Z

Hi,

On Thursday 09 November 2017 01:30 AM, Ville Syrjälä wrote:
> On Wed, Nov 08, 2017 at 10:39:59AM +0530, Mahesh Kumar wrote:
>> Hi,
>>
>>
>> On Tuesday 07 November 2017 11:57 PM, Chris Wilson wrote:
>>> clang spots
>>>
>>> drivers/gpu/drm/i915/intel_pm.c:4655:6: warning: variable 'trans_min' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>>> if (INTEL_GEN(dev_priv) >= 10)
>>>
>>> but fortunately for us we skip the function unless on a gen10+ device.
>>> However, to keep the function generic in case we do want to re-enable it
>>> for gen9 again, initialise trans_min to 0.
>>>
>>> References: ca47667f523e ("drm/i915/gen10: Calculate and enable transition WM")
>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
>>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>> Cc: Jani Nikula <jani.nikula@linux.intel.com>
>>> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>> ---
>>> drivers/gpu/drm/i915/intel_pm.c | 1 +
>>> 1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
>>> index b75c4cf074ff..40da5001be28 100644
>>> --- a/drivers/gpu/drm/i915/intel_pm.c
>>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>>> @@ -4652,6 +4652,7 @@ static void skl_compute_transition_wm(struct intel_crtc_state *cstate,
>>> if (!dev_priv->ipc_enabled)
>>> goto exit;
>>>
>>> + trans_min = 0;
>>> if (INTEL_GEN(dev_priv) >= 10)
>>> trans_min = 4;
>> BSpec WA section tells not to enable transition watermark for any GEN-9
>> platforms (that was the assumption with this patch)
>> But anyway trans_min value for GEN9 is 14 blocks, IMO adding else case
>> with trans_min = 14; will be logical solution to this.
> Bspec is telling me that 14 is the correct value for gen10 as well.
> Looks like the 4 came back from the future.
Thanks Ville for correcting this, I checked the BSpec again, yes for
gen-10 as well value is 14, looks like I read 4 instead of 14 earlier.
So we can always init trans_min = 14.

-Mahesh