Re: [PATCH v4 2/2] drm/i915/dp: Extend BDW DP audio workaround to GEN9 platforms

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

On Tue, 01 Nov 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com> wrote:
> According to BSpec, cdclk for BDW has to be not less than 432 MHz with DP
> audio enabled, port width x4, and link rate HBR2 (5.4 GHz). With cdclk less
> than 432 MHz, enabling audio leads to pipe FIFO underruns and displays
> cycling on/off.
>
> Let's apply this work around to GEN9 platforms too, as it fixes the same
> issue.

I'm too tired to read bspec now, but is gen9 really the answer, or just
Skylake?


>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97907
> Cc: stable@vger.kernel.org
> Cc: Libin Yang <libin.yang@linux.intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 37483ee..c0ae147 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10264,8 +10264,10 @@ static void bxt_modeset_commit_cdclk(struct drm_atomic_state *old_state)
>  static int bdw_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
>  					  int pixel_rate)
>  {
> +	struct drm_device *dev = crtc_state->base.crtc->dev;

Nitpick, I guess I'd make that

	struct drm_i915_private *dev_priv = to_i915(crtc_state->base.crtc->dev);

but no big deal.

> +
>  	/* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
> -	if (crtc_state->ips_enabled)
> +	if (IS_BROADWELL(to_i915(dev)) && crtc_state->ips_enabled)
>  		pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
>  
>  	/* BSpec says "Do not use DisplayPort with CDCLK less than
> @@ -10307,7 +10309,7 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
>  
>  		pixel_rate = ilk_pipe_pixel_rate(crtc_state);
>  
> -		if (IS_BROADWELL(dev_priv))
> +		if (IS_BROADWELL(dev_priv) || IS_GEN9(dev_priv))
>  			pixel_rate = bdw_adjust_min_pipe_pixel_rate(crtc_state,
>  								    pixel_rate);

-- 
Jani Nikula, Intel Open Source Technology Center