Re: [PATCH] drm/i915: VLV/CHV PSR: Increase wait delay time before active PSR.

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jul 27, 2015 at 06:37:28PM +0000, Vivi, Rodrigo wrote:
> On Mon, 2015-07-27 at 10:36 +0200, Daniel Vetter wrote:
> > On Fri, Jul 24, 2015 at 04:42:27PM -0700, Rodrigo Vivi wrote:
> > > Since active function on VLV immediately activate PSR let's give more
> > > time for idleness. Different from core platforms where we have idle_frames
> > > count.
> > > 
> > > Also kms_psr_sink_crc now is automated and always get this:
> > > 
> > > [drm:intel_enable_pipe] enabling pipe A
> > > [drm:intel_edp_backlight_on]
> > > [drm:intel_panel_enable_backlight] pipe
> > > [drm:intel_panel_enable_backlight] pipe A
> > > [drm:intel_panel_actually_set_backlight] set backlight PWM = 7812
> > > 
> > > PSR gets enabled somewhere here after backlight.
> > > 
> > > [drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x0
> > > [drm:vlv_pipe_set_fifo_size] Pipe A FIFO split 511 / 511 / 511
> > > [drm:vlv_update_wm] Setting FIFO watermarks - A: plane=391, cursor=63, sp
> > > 
> > > PSR gets flushed around here by intel_atomic_commit
> > > 
> > > [drm:vlv_pipe_set_fifo_size] Pipe A FIFO split 511 / 511 / 511
> > > [drm:vlv_update_wm] Setting FIFO watermarks - A: plane=391, cursor=63, sp
> > > [drm:intel_set_memory_cxsr] memory self-refresh is enabled
> > > [drm:intel_connector_check_state] [CONNECTOR:39:eDP-1]
> > > [drm:check_encoder_state] [ENCODER:30:DAC-30]
> > > [drm:check_encoder_state] [ENCODER:31:TMDS-31]
> > > [drm:check_encoder_state] [ENCODER:36:TMDS-36]
> > > [drm:check_encoder_state] [ENCODER:38:TMDS-38]
> > > [drm:check_crtc_state] [CRTC:21]
> > > [drm:check_crtc_state] [CRTC:26]
> > > [drm:intel_psr_activate [i915]] *ERROR* PSR Active
> > > [drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x
> > > [drm:intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR* pipe A underrun
> > > [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO
> > > Underrun.
> > > 
> > > It is true that in a product we won't keep disabling and enabling planes so
> > > frequently, but for safeness let's stay conservative.
> > > 
> > > It is also true that 500ms is an etternity. But PSR is anyway a power saving
> > > feature for idle scenario. So if it is idle feature stays on and 500ms to get
> > > it reanabled is not that insane.
> > > 
> > > v2: Rebase over intel_psr.c and fix typo.
> > > v3: Revival: Manual tests indicated that this is needed. With a short delay
> > >     there is a huge risk of getting blank screens when planes are being enabled.
> > > v4: Revival 2 with reasonable delay. 1/2 sec instead of 5. VBT is 10 sec but
> > >     actually time for link training what we aren't doing, but with only 100 sec
> > >     in some cases kms_psr_sink_crc manual was showing blank screen,
> > >     so let's use this for now. Also changed comment by a FIXME.
> > > v5: Rebase after a long time, remove FIXME and update comment above.
> > > v6: msecs_to_jiffies is already on delay. remove duplication.
> > > 
> > > Reviewed-by: Durgadoss R <durgadoss.r@intel.com> (v4)
> > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_psr.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
> > > index acd8ec8..bec13b8 100644
> > > --- a/drivers/gpu/drm/i915/intel_psr.c
> > > +++ b/drivers/gpu/drm/i915/intel_psr.c
> > > @@ -698,6 +698,7 @@ void intel_psr_flush(struct drm_device *dev,
> > >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > >  	struct drm_crtc *crtc;
> > >  	enum pipe pipe;
> > > +	int delay = msecs_to_jiffies(HAS_DDI(dev) ? 100 : 500);
> > 
> > Note that for a timeout you should be using our own
> > msecs_to_jiffies_timeout if it's for a timeout. This is needed since you
> > can't know when the next jiffy update happens and that might be right
> > away, therefore waiting for 10 jiffies might only be a wait for 9/HZ.
> > Anyway tiny nitpick.
> 
> This is actually only used on schedule_delayed_work that receives the
> numer of jiffies to wait.
> I believe to avoid confusion I should let the msecs_to_jiffies on
> schedule_delayed_work only and delay in ms. Do you want another v++?

If you feel like, was kinda just an aside bikeshed really. I'm just
constantly confused about jiffies timeouts myself ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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