[Intel-gfx] [PATCH 1/3] drm/i915: Improve PSR activation timing

[Chris Wilson]

Quoting Rodrigo Vivi (2018-02-28 00:14:08)
> From: Andy Lutomirski <luto at kernel.org>
> 
> The current PSR code has a two call sites that each schedule delayed
> work to activate PSR.  As far as I can tell, each call site intends
> to keep PSR inactive for the given amount of time and then allow it
> to be activated.
> 
> The call sites are:
> 
>  - intel_psr_enable(), which explicitly states in a comment that
>    it's trying to keep PSR off a short time after the dispay is
>    initialized as a workaround.
> 
>  - intel_psr_flush().  There isn't an explcit explanation, but the
>    intent is presumably to keep PSR off until the display has been
>    idle for 100ms.
> 
> The current code doesn't actually accomplish either of these goals.
> Rather than keeping PSR inactive for the given amount of time, it
> will schedule PSR for activation after the given time, with the
> earliest target time in such a request winning.
> 
> In other words, if intel_psr_enable() is immediately followed by
> intel_psr_flush(), then PSR will be activated after 100ms even if
> intel_psr_enable() wanted a longer delay.  And, if the screen is
> being constantly updated so that intel_psr_flush() is called once
> per frame at 60Hz, PSR will still be activated once every 100ms.
> 
> Rewrite the code so that it does what was intended.  This adds
> a new function intel_psr_schedule(), which will enable PSR after
> the requested time but no sooner.
> 
> v3: (by Rodrigo): Rebased on top of recent drm-tip without any
>     modification from the original.
> 
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> Signed-off-by: Andy Lutomirski <luto at kernel.org>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c |  9 +++--
>  drivers/gpu/drm/i915/i915_drv.h     |  4 ++-
>  drivers/gpu/drm/i915/intel_psr.c    | 69 ++++++++++++++++++++++++++++++++-----
>  3 files changed, 71 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 33fbf3965309..1ac942d1742e 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -2572,8 +2572,13 @@ static int i915_edp_psr_status(struct seq_file *m, void *data)
>         seq_printf(m, "Active: %s\n", yesno(dev_priv->psr.active));
>         seq_printf(m, "Busy frontbuffer bits: 0x%03x\n",
>                    dev_priv->psr.busy_frontbuffer_bits);
> -       seq_printf(m, "Re-enable work scheduled: %s\n",
> -                  yesno(work_busy(&dev_priv->psr.work.work)));
> +
> +       if (timer_pending(&dev_priv->psr.activate_timer))
> +               seq_printf(m, "Activate scheduled: yes, in %ldms\n",
> +                          (long)(dev_priv->psr.earliest_activate - jiffies) *

msecs_from_jiffies

> +                          1000 / HZ);
> +       else
> +               seq_printf(m, "Re-enable scheduled: no\n");
>  
>         if (HAS_DDI(dev_priv)) {
>                 if (dev_priv->psr.psr2_support)
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 7bbec5546d12..6e6cf2ce3749 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -764,7 +764,9 @@ struct i915_psr {
>         bool sink_support;
>         struct intel_dp *enabled;
>         bool active;
> -       struct delayed_work work;
> +       struct timer_list activate_timer;
> +       struct work_struct activate_work;
> +       unsigned long earliest_activate;

Incorporated into struct timer_list, so this is redundant.
-Chris