[Intel-gfx] [PATCH] drm/i915: HSW/BDW PSR Set idle_frames=2 since sometimes it can be off by 1.

[Runyan, Arthur J]

>From: Daniel Vetter 
>
>On Thu, Oct 30, 2014 at 05:35:55AM -0700, Rodrigo Vivi wrote:
>> It was identified that in some cases when moving cursor Hardware can do
>> mistake with idle_frame count. So Spec is being updated to use
>> 2 as minimum idle_frames.
>>
>> Reference:
>https://hsdhsw.intel.com/hsd/haswell_platform/default.aspx#sighting/default.as
>px?sighting_id=4394433
>> Cc: Arthur Runyan <arthur.j.runyan at intel.com>
>> Cc: Jani Nikula <jani.nikula at intel.com>
>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
>
>Since we have full-blown sw frontbuffer tracking: Do we care?
>
>I.e. is the effect of idle_frames = 1 that the hw will go bananas (bad, we
>want this patch) or that it might miss a cursor movement (no problem, the
>kernel will catch it anyway)?
>

The behavior will depend on the panel.  Going bananas is a possibility.
It also looks like VBT is being used to indicate that some panels have minimum idle frame requirements, so you really should be using VBT + 1 to ensure the hardware always outputs at least the VBT specified number of frames.


>Cheers, Daniel
>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 47e9d71..8cfbbc2 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -2178,7 +2178,7 @@ static void intel_edp_psr_enable_source(struct
>intel_dp *intel_dp)
>>  	struct drm_device *dev = dig_port->base.base.dev;
>>  	struct drm_i915_private *dev_priv = dev->dev_private;
>>  	uint32_t max_sleep_time = 0x1f;
>> -	uint32_t idle_frames = 1;
>> +	uint32_t idle_frames = 2; /* 2 is the minimum allowed */
>>  	uint32_t val = 0x0;
>>  	const uint32_t link_entry_time =
>EDP_PSR_MIN_LINK_ENTRY_TIME_8_LINES;
>>  	bool only_standby = false;
>> --
>> 1.9.3
>>