Re: [Intel-gfx] [v2] drm/i915/pps: improve eDP power on flow

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

On Tue, 01 Nov 2022, "Lee, Shawn C" <shawn.c.lee@intel.com> wrote:
> On Tuesday, November 1, 2022 5:53 PM, Jani Nikula <jani.nikula@linux.intel.com> wrote:
>>On Mon, 24 Oct 2022, Lee Shawn C <shawn.c.lee@intel.com> wrote:
>>> A panel power off cycle delay always append before turn eDP on.
>>> Driver should check last_power_on and last_backlight_off before insert 
>>> this delay. If these values are the same, it means eDP was off until 
>>> now and driver can bypass power off cycle delay to save some times to 
>>> speed up eDP power on sequence.
>>>
>>> v2: fix commit messages
>>
>>There are more changes here than what the changelog says, but the previous review comments were not answered [1].
>>
>
> I'm sorry that lose the question in [1]. 
>
> "But someone else may have turned it off just before we were handed control, we have no idea."
> This is the situation from Ville's comment. Agree that we don't know when panel will be powered off.
> In my opinion, eDP panel should not be turned off before i915 take it over. If it was turned on or off by standard contorl (ex: modeset).
> last_power_on and last_backlight_off would not be the same. So this change should be safe.

I think it's pretty much a hard requirement we respect the panel delays
at i915 probe. If we don't know, we don't know, and we can't make
assumptions.

If the goal is to speed up boot, you should ensure 1) the pre-os enables
the display, and 2) i915 can take over the display without a modeset and
a panel power cycle.


BR,
Jani.


>
> Best regards,
> Shawn
>
>>
>>BR,
>>Jani.
>>
>>
>>[1] https://lore.kernel.org/r/Y1afUdAwfVTACJoK@intel.com
>>
>>>
>>> Cc: Shankar Uma <uma.shankar@intel.com>
>>> Cc: Jani Nikula <jani.nikula@linux.intel.com>
>>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
>>> ---
>>>  drivers/gpu/drm/i915/display/intel_pps.c | 9 ++++++++-
>>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/display/intel_pps.c 
>>> b/drivers/gpu/drm/i915/display/intel_pps.c
>>> index 21944f5bf3a8..290473ec70d5 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_pps.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_pps.c
>>> @@ -509,6 +509,13 @@ static void wait_panel_power_cycle(struct intel_dp *intel_dp)
>>>  	ktime_t panel_power_on_time;
>>>  	s64 panel_power_off_duration;
>>>  
>>> +	/* When last_power_on equal to last_backlight_off, it means driver did not
>>> +	 * turn on or off eDP panel so far. So we can bypass power cycle delay to
>>> +	 * save some times here.
>>> +	 */
>>> +	if (intel_dp->pps.last_power_on == intel_dp->pps.last_backlight_off)
>>> +		return;
>>> +
>>>  	drm_dbg_kms(&i915->drm, "Wait for panel power cycle\n");
>>>  
>>>  	/* take the difference of current time and panel power off time @@ 
>>> -1100,7 +1107,7 @@ static void pps_init_timestamps(struct intel_dp 
>>> *intel_dp)  {
>>>  	intel_dp->pps.panel_power_off_time = ktime_get_boottime();
>>>  	intel_dp->pps.last_power_on = jiffies;
>>> -	intel_dp->pps.last_backlight_off = jiffies;
>>> +	intel_dp->pps.last_backlight_off = intel_dp->pps.last_power_on;
>>>  }
>>>  
>>>  static void
>>
>>--
>>Jani Nikula, Intel Open Source Graphics Center

-- 
Jani Nikula, Intel Open Source Graphics Center