linux-kernel - Re: [PATCH v5 4/6] drm: rcar-du: lvds: Allow for even and odd pixels swap

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Message-ID: <20191216213451.GH4856@pendragon.ideasonboard.com>
Date:   Mon, 16 Dec 2019 23:34:51 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Fabrizio Castro <fabrizio.castro@...renesas.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sean Paul <sean@...rly.run>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        ebiharaml@...linux.co.jp
Subject: Re: [PATCH v5 4/6] drm: rcar-du: lvds: Allow for even and odd pixels
 swap

Hi Fabrizio,

Thank you for the patch.

On Mon, Dec 16, 2019 at 08:12:32PM +0000, Fabrizio Castro wrote:
> DT properties dual-lvds-even-pixels and dual-lvds-odd-pixels
> can be used to work out if the driver needs to swap even
> and odd pixels around.
> 
> This patch makes use of the return value from function
> drm_of_lvds_get_dual_link_pixel_order to determine if we
> need to swap odd and even pixels around for things to work
> properly.
> 
> Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> 
> ---
> v4->v5:
> * Addressed comments from Laurent's review
> 
> v3->v4:
> * New patch extracted from patch:
>   "drm: rcar-du: lvds: Add dual-LVDS panels support"
> ---
>  drivers/gpu/drm/rcar-du/rcar_lvds.c | 67 +++++++++++++++++++++++++++++--------
>  1 file changed, 53 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> index 3eb208e..c6a38c3 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> @@ -37,6 +37,12 @@ enum rcar_lvds_mode {
>  	RCAR_LVDS_MODE_VESA = 4,
>  };
>  
> +enum rcar_lvds_link_type {
> +	RCAR_LVDS_SINGLE_LINK = 0,
> +	RCAR_LVDS_DUAL_LINK_EVEN_ODD_PIXELS = 1,
> +	RCAR_LVDS_DUAL_LINK_ODD_EVEN_PIXELS = 2,
> +};
> +
>  #define RCAR_LVDS_QUIRK_LANES		BIT(0)	/* LVDS lanes 1 and 3 inverted */
>  #define RCAR_LVDS_QUIRK_GEN3_LVEN	BIT(1)	/* LVEN bit needs to be set on R8A77970/R8A7799x */
>  #define RCAR_LVDS_QUIRK_PWD		BIT(2)	/* PWD bit available (all of Gen3 but E3) */
> @@ -67,7 +73,7 @@ struct rcar_lvds {
>  	} clocks;
>  
>  	struct drm_bridge *companion;
> -	bool dual_link;
> +	enum rcar_lvds_link_type dual_link;

Do you think we should rename this to link_type (and test for
lvds->link_type != RCAR_LVDS_SINGLE_LINK) instead of lvds->dual_link) ?
Apart from that,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

>  };
>  
>  #define bridge_to_rcar_lvds(b) \
> @@ -484,12 +490,31 @@ static void rcar_lvds_atomic_enable(struct drm_bridge *bridge,
>  	rcar_lvds_write(lvds, LVDCHCR, lvdhcr);
>  
>  	if (lvds->info->quirks & RCAR_LVDS_QUIRK_DUAL_LINK) {
> -		/*
> -		 * Configure vertical stripe based on the mode of operation of
> -		 * the connected device.
> -		 */
> -		rcar_lvds_write(lvds, LVDSTRIPE,
> -				lvds->dual_link ? LVDSTRIPE_ST_ON : 0);
> +		u32 lvdstripe = 0;
> +
> +		if (lvds->dual_link) {
> +			/*
> +			 * By default we generate even pixels from the primary
> +			 * encoder and odd pixels from the companion encoder.
> +			 * Swap pixels around if the sink requires odd pixels
> +			 * from the primary encoder and even pixels from the
> +			 * companion encoder.
> +			 */
> +			bool swap_pixels = lvds->dual_link ==
> +				RCAR_LVDS_DUAL_LINK_ODD_EVEN_PIXELS;
> +
> +			/*
> +			 * Configure vertical stripe since we are dealing with
> +			 * an LVDS dual-link connection.
> +			 *
> +			 * ST_SWAP is reserved for the companion encoder, only
> +			 * set it in the primary encoder.
> +			 */
> +			lvdstripe = LVDSTRIPE_ST_ON
> +				  | (lvds->companion && swap_pixels ?
> +				     LVDSTRIPE_ST_SWAP : 0);
> +		}
> +		rcar_lvds_write(lvds, LVDSTRIPE, lvdstripe);
>  	}
>  
>  	/*
> @@ -716,15 +741,26 @@ static int rcar_lvds_parse_dt_companion(struct rcar_lvds *lvds)
>  	of_node_put(port0);
>  	of_node_put(port1);
>  
> -	if (dual_link >= DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS)
> -		lvds->dual_link = true;
> -	else if (lvds->next_bridge && lvds->next_bridge->timings)
> +	switch (dual_link) {
> +	case DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS:
> +		lvds->dual_link = RCAR_LVDS_DUAL_LINK_ODD_EVEN_PIXELS;
> +		break;
> +	case DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS:
> +		lvds->dual_link = RCAR_LVDS_DUAL_LINK_EVEN_ODD_PIXELS;
> +		break;
> +	default:
>  		/*
>  		 * Early dual-link bridge specific implementations populate the
> -		 * timings field of drm_bridge, read the dual_link flag off the
> -		 * bridge directly for backward compatibility.
> +		 * timings field of drm_bridge. If the flag is set, we assume
> +		 * that we are expected to generate even pixels from the primary
> +		 * encoder, and odd pixels from the companion encoder.
>  		 */
> -		lvds->dual_link = lvds->next_bridge->timings->dual_link;
> +		if (lvds->next_bridge && lvds->next_bridge->timings &&
> +		    lvds->next_bridge->timings->dual_link)
> +			lvds->dual_link = RCAR_LVDS_DUAL_LINK_EVEN_ODD_PIXELS;
> +		else
> +			lvds->dual_link = RCAR_LVDS_SINGLE_LINK;
> +	}
>  
>  	if (!lvds->dual_link) {
>  		dev_dbg(dev, "Single-link configuration detected\n");
> @@ -741,6 +777,9 @@ static int rcar_lvds_parse_dt_companion(struct rcar_lvds *lvds)
>  		"Dual-link configuration detected (companion encoder %pOF)\n",
>  		companion);
>  
> +	if (lvds->dual_link == RCAR_LVDS_DUAL_LINK_ODD_EVEN_PIXELS)
> +		dev_dbg(dev, "Data swapping required\n");
> +
>  	/*
>  	 * FIXME: We should not be messing with the companion encoder private
>  	 * data from the primary encoder, we should rather let the companion
> @@ -751,7 +790,7 @@ static int rcar_lvds_parse_dt_companion(struct rcar_lvds *lvds)
>  	 * for the time being.
>  	 */
>  	companion_lvds = bridge_to_rcar_lvds(lvds->companion);
> -	companion_lvds->dual_link = true;
> +	companion_lvds->dual_link = lvds->dual_link;
>  
>  done:
>  	of_node_put(companion);

-- 
Regards,

Laurent Pinchart