[PATCH 2/4] drm/i915/dsi: Enable dithering for 6 bpc panels

[Ville Syrjälä]

On Sat, Dec 01, 2018 at 12:31:46PM +0100, Hans de Goede wrote:
> The display engine has 2 dithering enable bits which both need to be set
> for dithering to happen, 1 in the PIPECONF register which is taken care of
> by i9xx_set_pipeconf() and a second bit at the encoder level.
> 
> The dsi code was not setting the encoder level dithering enable bit causing
> dithering to be disabled, this commit fixes this.
> 
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
>  drivers/gpu/drm/i915/vlv_dsi.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/vlv_dsi.c b/drivers/gpu/drm/i915/vlv_dsi.c
> index c10def5efa22..c21cbfa9653c 100644
> --- a/drivers/gpu/drm/i915/vlv_dsi.c
> +++ b/drivers/gpu/drm/i915/vlv_dsi.c
> @@ -711,6 +711,10 @@ static void intel_dsi_port_enable(struct intel_encoder *encoder,
>  					LANE_CONFIGURATION_DUAL_LINK_B :
>  					LANE_CONFIGURATION_DUAL_LINK_A;
>  		}
> +
> +		if (intel_dsi->pixel_format != MIPI_DSI_FMT_RGB888)
> +			temp |= DITHERING_ENABLE;

The docs say this was only made to work in C0 stepping. Not sure any
BYT-Ts were ever shipped with B2/3, nor am I sure if setting the bit
would have any effect there. IMO let's just set the bit and hope for
the best.

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> +
>  		/* assert ip_tg_enable signal */
>  		I915_WRITE(port_ctrl, temp | DPI_ENABLE);
>  		POSTING_READ(port_ctrl);
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel