linux-kernel - Re: [PATCH/RFC 05/12] drm: rcar-du: lvds: Add data swap support

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Date:   Fri, 2 Aug 2019 11:06:13 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Fabrizio Castro <fabrizio.castro@...renesas.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Simon Horman <horms@...ge.net.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>
Subject: Re: [PATCH/RFC 05/12] drm: rcar-du: lvds: Add data swap support

Hi Fabrizio,

Thank you for the patch.

On Fri, Aug 02, 2019 at 08:34:02AM +0100, Fabrizio Castro wrote:
> When in vertical stripe mode of operation, there is the option
> of swapping even data and odd data on the two LVDS interfaces
> used to drive the video output.
> Add data swap support by exposing a new DT property named
> "renesas,swap-data".
> 
> Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> ---
>  drivers/gpu/drm/rcar-du/rcar_lvds.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> index 3aeaf9e..c306fab 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> @@ -69,6 +69,7 @@ struct rcar_lvds {
>  
>  	struct drm_bridge *companion;
>  	bool dual_link;
> +	bool stripe_swap_data;
>  };
>  
>  #define bridge_to_rcar_lvds(bridge) \
> @@ -439,12 +440,16 @@ static void rcar_lvds_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)
> +			/*
> +			 * Configure vertical stripe based on the mode of
> +			 * operation of the connected device.
> +			 */
> +			lvdstripe = LVDSTRIPE_ST_ON | (lvds->stripe_swap_data ?
> +						       LVDSTRIPE_ST_SWAP : 0);

Would the following be simpler ?

		lvdstripe = (lvds->dual_link ? LVDSTRIPE_ST_ON : 0)
			  | (lvds->stripe_swap_data ? LVDSTRIPE_ST_SWAP : 0);

> +		rcar_lvds_write(lvds, LVDSTRIPE, lvdstripe);
>  	}
>  
>  	/*
> @@ -770,8 +775,12 @@ static int rcar_lvds_parse_dt(struct rcar_lvds *lvds)
>  		}
>  	}
>  
> -	if (lvds->dual_link)
> +	if (lvds->dual_link) {
> +		lvds->stripe_swap_data = of_property_read_bool(
> +						lvds->dev->of_node,
> +						"renesas,swap-data");
>  		ret = rcar_lvds_parse_dt_companion(lvds);
> +	}

As explained in the review of the corresponding DT bindings, I think
this should be queried from the remote device rather than specified in
DT.

>  
>  done:
>  	of_node_put(local_output);

-- 
Regards,

Laurent Pinchart