Re: [PATCH v4 4/7] drm: rcar-du: lvds: Allow for even and odd pixels swap

[Laurent Pinchart]

Hi Fabrizio,

Thank you for the patch.

On Fri, Dec 06, 2019 at 04:32:51PM +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@xxxxxxxxxxxxxx>
> 
> ---
> v3->v4:
> * New patch extracted from patch:
>   "drm: rcar-du: lvds: Add dual-LVDS panels support"
> ---
>  drivers/gpu/drm/rcar-du/rcar_lvds.c | 46 +++++++++++++++++++++++++++++--------
>  1 file changed, 37 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> index 6c1f171..cb2147c 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
> @@ -71,6 +71,7 @@ struct rcar_lvds {
>  
>  	struct drm_bridge *companion;
>  	bool dual_link;
> +	bool stripe_swap_data;

Should we merge those two fields in an int dual_link that would be set
to DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS,
DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS or a negative value (or maybe we the
value of enum drm_lvds_dual_link_pixels could be modified so that 0
could mean single link) ?

>  };
>  
>  #define bridge_to_rcar_lvds(b) \
> @@ -441,12 +442,20 @@ 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.
> +			 *
> +			 * ST_SWAP from LVD1STRIPE is reserved, do not set
> +			 * in the companion LVDS

Maybe "ST_SWAP is reserved for the companion encoder, only set it in the
primary encoder." ?

> +			 */
> +			lvdstripe = LVDSTRIPE_ST_ON |
> +				(lvds->companion && lvds->stripe_swap_data ?
> +				 LVDSTRIPE_ST_SWAP : 0);

To match the coding style of the rest of the driver,

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

Even though not strictly required, could you surround this statement
with { } as it spans quite a few lines with the comment ?

> +		rcar_lvds_write(lvds, LVDSTRIPE, lvdstripe);
>  	}
>  
>  	/*
> @@ -702,17 +711,33 @@ static int rcar_lvds_parse_dt_companion(struct rcar_lvds *lvds)
>  	dual_link = drm_of_lvds_get_dual_link_pixel_order(p0, p1);
>  	of_node_put(p0);
>  	of_node_put(p1);
> -	if (dual_link >= DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS) {
> +
> +	switch (dual_link) {
> +	case DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS:
> +		/*
> +		 * By default we generate even pixels from this encoder and odd
> +		 * pixels from the companion encoder, but since p0 is connected
> +		 * to the port expecting ood pixels, and p1 is connected to the
> +		 * port expecting even pixels, we need to swap even and odd
> +		 * pixels around.
> +		 */
> +		lvds->stripe_swap_data = true;
> +		lvds->dual_link = true;
> +		break;
> +	case DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS:
>  		lvds->dual_link = true;
> -	} else if (lvds->next_bridge && lvds->next_bridge->timings) {
> +		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.
>  		 */
> -		lvds->dual_link = lvds->next_bridge->timings->dual_link;
> +		if (lvds->next_bridge && lvds->next_bridge->timings)
> +			lvds->dual_link = lvds->next_bridge->timings->dual_link;
>  	}
>  
> +

A single blank line is enough.

>  	if (!lvds->dual_link) {
>  		dev_dbg(dev, "Single-link configuration detected\n");
>  		goto done;
> @@ -728,6 +753,9 @@ static int rcar_lvds_parse_dt_companion(struct rcar_lvds *lvds)
>  		"Dual-link configuration detected (companion encoder %pOF)\n",
>  		companion);
>  
> +	if (lvds->stripe_swap_data)
> +		dev_dbg(dev, "Data swapping required\n");
> +
>  	companion_lvds = bridge_to_rcar_lvds(lvds->companion);
>  
>  	/*

-- 
Regards,

Laurent Pinchart