linux-kernel - Re: [PATCH RFC v2 3/8] drm/bridge: synopsys: dw-hdmi: add bus format negociation

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Date:   Tue, 27 Aug 2019 11:03:56 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     a.hajda@...sung.com, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...l.net,
        linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 3/8] drm/bridge: synopsys: dw-hdmi: add bus
 format negociation

On Tue, 27 Aug 2019 10:14:20 +0200
Neil Armstrong <narmstrong@...libre.com> wrote:

> Add the atomic_get_output_bus_fmts, atomic_get_input_bus_fmts to negociate

								   ^negotiate

> the possible output and input formats for the current mode and monitor,
> and use the negociated formats in a basic atomic_check callback.

	      ^negotiated

> 
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> ---


>  
> +static void dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
> +					struct drm_bridge_state *bridge_state,
> +					struct drm_crtc_state *crtc_state,
> +					struct drm_connector_state *conn_state,
> +					unsigned int *num_output_fmts,
> +					u32 *output_fmts)
> +{
> +	struct drm_connector *conn = conn_state->connector;
> +	struct drm_display_info *info = &conn->display_info;
> +	struct drm_display_mode *mode = &crtc_state->mode;
> +	bool is_hdmi2_sink = info->hdmi.scdc.supported;	
> +	int i = 0;
> +
> +	/*
> +	 * If the current mode enforces 4:2:0, force the output but format
> +	 * to 4:2:0 and do not add the YUV422/444/RGB formats
> +	 */
> +	if (drm_mode_is_420_only(info, mode) ||
> +	    (!is_hdmi2_sink && drm_mode_is_420_also(info, mode))) {
> +
> +		/* Order bus formats from 16bit to 8bit if supported */
> +		if (info->bpc == 16 &&
> +		    (info->hdmi.y420_dc_modes & DRM_EDID_YCBCR420_DC_48)) {
> +			if (output_fmts)
> +				output_fmts[i] = MEDIA_BUS_FMT_UYYVYY16_0_5X48;
> +			++i;
> +		}

You could probably add the following helper:

static void dw_hdmi_bridge_add_fmt(unsigned int *num_fmts, u32 *fmts,
				   u32 new_fmt)
{
	if (fmts)
		fmts[*num_fmts] = new_fmt;

	(*num_fmts)++;
}

to avoid duplicating the

	if (fmts)
		...

	i++;			

logic.