Re: [PATCH v3 07/10] drm: rcar-du: Skip LVDS1 output on Gen3 when using dual-link LVDS mode

[Sam Ravnborg <sam@ravnborg.org>]

Hi Laurent.

On Tue, May 28, 2019 at 07:50:52PM +0300, Laurent Pinchart wrote:
> Hi Sam,
> 
> On Tue, May 28, 2019 at 06:42:13PM +0200, Sam Ravnborg wrote:
> > On Tue, May 28, 2019 at 05:12:31PM +0300, Laurent Pinchart wrote:
> > > In dual-link LVDS mode, the LVDS1 encoder is used as a companion for
> > > LVDS0, and both encoders transmit data from DU0. The LVDS1 output of DU1
> > > can't be used in that case, don't create an encoder and connector for
> > > it.
> > > 
> > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> > > Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > > Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > > ---
> > > Changess since v2:
> > > 
> > > - Remove unneeded bridge NULL check
> > > ---
> > >  drivers/gpu/drm/rcar-du/rcar_du_encoder.c | 12 ++++++++++++
> > >  drivers/gpu/drm/rcar-du/rcar_du_kms.c     |  2 +-
> > >  2 files changed, 13 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_encoder.c b/drivers/gpu/drm/rcar-du/rcar_du_encoder.c
> > > index 6c91753af7bc..0f00bdfe2366 100644
> > > --- a/drivers/gpu/drm/rcar-du/rcar_du_encoder.c
> > > +++ b/drivers/gpu/drm/rcar-du/rcar_du_encoder.c
> > > @@ -16,6 +16,7 @@
> > >  #include "rcar_du_drv.h"
> > >  #include "rcar_du_encoder.h"
> > >  #include "rcar_du_kms.h"
> > > +#include "rcar_lvds.h"
> > >  
> > >  /* -----------------------------------------------------------------------------
> > >   * Encoder
> > > @@ -97,6 +98,17 @@ int rcar_du_encoder_init(struct rcar_du_device *rcdu,
> > >  		}
> > >  	}
> > >  
> > > +	/*
> > > +	 * On Gen3 skip the LVDS1 output if the LVDS1 encoder is used as a
> > > +	 * companion for LVDS0 in dual-link mode.
> > > +	 */
> > > +	if (rcdu->info->gen >= 3 && output == RCAR_DU_OUTPUT_LVDS1) {
> > 
> > Both subject and comment above says "On Gen3", but the code looks like
> > it implements "On Gen3 or newer" - due to use of ">=".
> > Looks wrong to me.
> 
> Gen3 is the newest generation :-) We thus use >= through the DU and LVDS
> drivers to prepare for support of Gen4, just in case.
OK, but I guess we agree that the comment needs a small update them.

Actually I implicitly reads that it is only from Gen3 onwards that the
LVDS1 encoder can be used as a companion.
My initial understanding reading the comment was that this implmented a
workaround for Gen3 - but it is a workarounf for missing features in
older than Gen3.
So, assuming this is correct, when trying to specify a companion on
older then Gen3 should result in some kind of error/warning?
(Maybe it does).

	Sam