Re: [PATCH 2/2] drm/i915/dp: Validate mode against max. link data rate for DP MST

[Manasi Navare <manasi.d.navare@intel.com>]

On Wed, Nov 09, 2016 at 09:32:30PM -0800, Dhinakaran Pandiyan wrote:
> Not validating the the mode rate against link rate results not pruning
> invalid modes. For e.g, HBR2 5.4 Gpbs 2 lane configuration does not
> support 4k @ 60Hz. But, we do not reject this mode currently.
> 
> So, make use of the helpers in intel_dp in validate mode rates against
> max. data rate of a configuration.
> 
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c     |  4 ++--
>  drivers/gpu/drm/i915/intel_dp_mst.c | 12 +++++++++++-
>  drivers/gpu/drm/i915/intel_drv.h    |  2 ++
>  3 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 7a9e122..7a73e43 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -161,14 +161,14 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
>  	return min(source_max, sink_max);
>  }
>  
> -static int
> +int
>  intel_dp_link_required(int pixel_clock, int bpp)
>  {
>  	/* pixel_clock is in kHz, divide bpp by 8 to return the value in kBps*/
>  	return (pixel_clock * bpp + 7) / 8;
>  }
>  
> -static int
> +int
>  intel_dp_max_data_rate(int max_link_clock, int max_lanes)
>  {
>  	/* max_link_clock is the link symbol clock (LS_Clk) in kHz and not the
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index 3ffbd69..38d2ce0 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -335,7 +335,17 @@ static enum drm_mode_status
>  intel_dp_mst_mode_valid(struct drm_connector *connector,
>  			struct drm_display_mode *mode)
>  {
> +	struct intel_connector *intel_connector = to_intel_connector(connector);
> +	struct intel_dp *intel_dp = intel_connector->mst_port;
>  	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
> +	int link_clock = intel_dp_max_link_rate(intel_dp);
> +	int lane_count = drm_dp_max_lane_count(intel_dp->dpcd);
> +	int bpp = 24; /* MST uses fixed bpp */
> +	int mode_rate;
> +	int link_max_data_rate;

In the SST equivalent mode_valid function, this variable is named as
max_rate, I think you should name it as max_rate as well for consistency.
Other than that this looks good, we definitely need this for mode validation
at an early stage.

Regards
Manasi

> +
> +	link_max_data_rate = intel_dp_max_data_rate(link_clock, lane_count);
> +	mode_rate = intel_dp_link_required(mode->clock, bpp);
>  
>  	/* TODO - validate mode against available PBN for link */
>  	if (mode->clock < 10000)
> @@ -344,7 +354,7 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
>  	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
>  		return MODE_H_ILLEGAL;
>  
> -	if (mode->clock > max_dotclk)
> +	if (mode_rate > link_max_data_rate || mode->clock > max_dotclk)
>  		return MODE_CLOCK_HIGH;
>  
>  	return MODE_OK;
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index c2f3863..313419d 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1471,6 +1471,8 @@ bool intel_dp_read_dpcd(struct intel_dp *intel_dp);
>  bool __intel_dp_read_desc(struct intel_dp *intel_dp,
>  			  struct intel_dp_desc *desc);
>  bool intel_dp_read_desc(struct intel_dp *intel_dp);
> +int intel_dp_link_required(int pixel_clock, int bpp);
> +int intel_dp_max_data_rate(int max_link_clock, int max_lanes);
>  
>  /* intel_dp_aux_backlight.c */
>  int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector);
> -- 
> 2.7.4
> 
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