[Intel-gfx] [PATCH] drm/i915: Suspend resume timing optimization.

[Paulo Zanoni]

2015-12-07 18:28 GMT-02:00  <abhay.kumar at intel.com>:
> From: Abhay Kumar <abhay.kumar at intel.com>
>
> Moving 250ms from T12 timing to suspend path so that
> resume path will be faster.

Can you please elaborate more on your motivation for this patch? I'm a
little confused. You're trying to make resume faster by making suspend
slower? What are your main arguments for this?

>
> Signed-off-by: Abhay Kumar <abhay.kumar at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 7f618cf..2679c9e 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -2389,6 +2389,12 @@ static void intel_ddi_post_disable(struct intel_encoder *intel_encoder)

Funcion intel_ddi_post_disable() doesn't only run on suspend
situations, yet your commit message suggests you're optimizing
suspend. Maybe this commit makes non-suspend modesets slower because
now we need to wait the panel power cycle earlier? Have you measured
the possible downsides?

>                 intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
>                 intel_edp_panel_vdd_on(intel_dp);
>                 intel_edp_panel_off(intel_dp);
> +
> +               /* Give additional delay of 250 ms so that resume time will
> +                  be faster and also meets T12 delay.
> +               */

The comment says 250ms, but the code doesn't. Also, there's a missing
'*' char in the comment.

> +               wait_remaining_ms_from_jiffies(intel_dp->last_power_cycle,
> +                                      (intel_dp->panel_power_cycle_delay/2));

Why wait half the panel power cycle? Why did you choose exactly this value?

Thanks,
Paulo

>         }
>
>         if (IS_SKYLAKE(dev) || IS_KABYLAKE(dev))
> --
> 1.9.1
>
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-- 
Paulo Zanoni