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

[Fabrizio Castro <fabrizio.castro@bp.renesas.com>]

Hi Laurent,

Thank you for your feedback!

> From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Sent: 02 August 2019 09:06
> 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@bp.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);

I actually think I need to rework this patch slightly, because the user manual
says that ST_SWAP is reserved for LVD1STRIPE, so I need to make sure we
don't set it for LVDS1.

So perhaps, this could translate to something like:
If (lvds->dual_link)
	lvdstripe = LVDSTRIPE_ST_ON | (<swap-whatever> && lvds->companion) ? LVDSTRIPE_ST_SWAP : 0);

I don't think we should be setting LVDSTRIPE_ST_SWAP without LVDSTRIPE_ST_ON, this solution
would allow us to test lvds->dual_link only once, and will prevent us from setting LVDSTRIPE_ST_SWAP if
LVDSTRIPE_ST_ON is not set or if we are touching LVDS1.

What do you think?

Thanks,
Fab

> >  	}
> >
> >  	/*
> > @@ -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