Re: [v1 6/6] drm/i915/display: Reduce blanking to support 4k60@10bpp for LSPCON

Ville Syrjälä
2019-10-16T13:13:40Z

On Wed, Oct 16, 2019 at 04:02:49PM +0530, Uma Shankar wrote:
> Blanking needs to be reduced to incorporate DP and HDMI timing/link
> bandwidth limitations for CEA modes (4k@60 at 10 bpp). DP can drive
> 17.28Gbs while 4k modes (VIC97 etc) at 10 bpp required 17.8 Gbps.
> This will cause mode to blank out. Reduced Htotal by shortening the
> back porch and front porch within permissible limits.
>
> Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index d92777bd3bed..a12b6916023d 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -597,8 +597,10 @@ intel_dp_mode_valid(struct drm_connector *connector,
> {
> struct intel_dp *intel_dp = intel_attached_dp(connector);
> struct intel_connector *intel_connector = to_intel_connector(connector);
> + struct intel_encoder *intel_encoder = intel_attached_encoder(connector);
> struct drm_display_mode *fixed_mode = intel_connector->panel.fixed_mode;
> struct drm_i915_private *dev_priv = to_i915(connector->dev);
> + struct intel_lspcon *lspcon = enc_to_intel_lspcon(&intel_encoder->base);
> int target_clock = mode->clock;
> int max_rate, mode_rate, max_lanes, max_link_clock;
> int max_dotclk;
> @@ -620,6 +622,21 @@ intel_dp_mode_valid(struct drm_connector *connector,
> target_clock = fixed_mode->clock;
> }
>
> + /*
> + * Reducing Blanking to incorporate DP and HDMI timing/link bandwidth
> + * limitations for CEA modes (4k@60 at 10 bpp). DP can drive 17.28Gbs
> + * while 4k modes (VIC97 etc) at 10 bpp required 17.8 Gbps. This will
> + * cause mode to blank out. Reduced Htotal by shortening the back porch
> + * and front porch within permissible limits.
> + */
> + if (lspcon->active && lspcon->hdr_supported &&
> + mode->clock > 570000) {
> + mode->clock = 570000;
> + mode->htotal -= 180;
> + mode->hsync_start -= 72;
> + mode->hsync_end -= 72;
> + }

I don't think we want these kind of hacks. Either the mode works or it
doesn't.

> +
> max_link_clock = intel_dp_max_link_rate(intel_dp);
> max_lanes = intel_dp_max_lane_count(intel_dp);
>
> --
> 2.22.0

--
Ville Syrjälä
Intel