Re: [PATCH] drm/i915: Pretend cursor is always on for ILK-style WM calculations

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Feb 01, 2016 at 01:26:14AM -0800, Matt Roper wrote:
> Due to our lack of two-step watermark programming, our driver has
> historically pretended that the cursor plane is always on for the
> purpose of watermark calculations; this helps avoid serious flickering
> when the cursor turns off/on (e.g., when the user moves the mouse
> pointer to a different screen).  That workaround was accidentally
> dropped as we started working toward atomic watermark updates.  Since we
> still aren't quite there yet with two-stage updates, we need to
> resurrect the workaround and treat the cursor as always active.
> 
> Cc: simdev11@outlook.com
> Cc: manfred.kitzbichler@gmail.com
> Reported-by: simdev11@outlook.com
> Reported-by: manfred.kitzbichler@gmail.com
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93892
> Fixes: 43d59eda1 ("drm/i915: Eliminate usage of plane_wm_parameters from ILK-style WM code (v2)")
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> ---
> I'm traveling at the moment and don't have any HW access, so this patch is
> completely untested, but I think it will solve the issue being reported.
> 
>  drivers/gpu/drm/i915/intel_pm.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 31bc4ea..a53c018 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -1799,16 +1799,21 @@ static uint32_t ilk_compute_cur_wm(const struct intel_crtc_state *cstate,
>  				   const struct intel_plane_state *pstate,
>  				   uint32_t mem_value)
>  {
> -	int cpp = pstate->base.fb ?
> -		drm_format_plane_cpp(pstate->base.fb->pixel_format, 0) : 0;
> +	/*
> +	 * We treat the cursor plane as always-on for the purposes of watermark
> +	 * calculation.  Until we have two-stage watermark programming merged,
> +	 * this is necessary to avoid flickering.
> +	 */
> +	int cpp = 4;
> +	int width = drm_rect_width(&pstate->dst) ?: 64;

I don't think we can rely on that being correct when the plane is not
visible. Also for the cursor, I'm not sure we should be even using the
visible width of the plane when it's partially visible.

>  
> -	if (!cstate->base.active || !pstate->visible)
> +	if (!cstate->base.active)
>  		return 0;
>  
> +
>  	return ilk_wm_method2(ilk_pipe_pixel_rate(cstate),
>  			      cstate->base.adjusted_mode.crtc_htotal,
> -			      drm_rect_width(&pstate->dst),
> -			      cpp, mem_value);
> +			      width, cpp, mem_value);
>  }
>  
>  /* Only for WM_LP. */
> -- 
> 2.1.4
> 
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-- 
Ville Syrjälä
Intel OTC
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