diff mbox series

[6/7] drm/vc4: dpi: Change the default DPI format to being 18bpp, not 24.

Message ID 20221013-rpi-dpi-improvements-v1-6-8a7a96949cb0@cerno.tech
State New
Headers
Series drm/vc4: dpi: Various improvements |

Commit Message

Maxime Ripard Oct. 13, 2022, 9:56 a.m. UTC 
  From: Dave Stevenson <dave.stevenson@raspberrypi.com>

DPI hasn't really been used up until now, so the default has
been meaningless.
In theory we should be able to pass the desired format for the
adjacent bridge chip through, but framework seems to be missing
for that.

As the main device to use DPI is the VGA666 or Adafruit Kippah,
both of which use RGB666, change the default to being RGB666 instead
of RGB888.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_dpi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Laurent Pinchart Oct. 15, 2022, 5:13 p.m. UTC | #1 
Hi Maxime (and Dave),

Thank you for the patch.

On Thu, Oct 13, 2022 at 11:56:50AM +0200, Maxime Ripard wrote:
> From: Dave Stevenson <dave.stevenson@raspberrypi.com>
> 
> DPI hasn't really been used up until now, so the default has
> been meaningless.
> In theory we should be able to pass the desired format for the
> adjacent bridge chip through, but framework seems to be missing
> for that.

Doesn't the bridge infrastructure allow that ? Or maybe this commit
message was written a while ago, before it was possible ?

In any case, it would be nice to use the bus format exposed by the next
bridge in the chain, but that can be done in a subsequent step. The new
default seems reasonable.

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

> As the main device to use DPI is the VGA666 or Adafruit Kippah,
> both of which use RGB666, change the default to being RGB666 instead
> of RGB888.
> 
> Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---
>  drivers/gpu/drm/vc4/vc4_dpi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
> index ecbe4cd87036..fdae02760b6d 100644
> --- a/drivers/gpu/drm/vc4/vc4_dpi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dpi.c
> @@ -150,8 +150,8 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
>  	}
>  	drm_connector_list_iter_end(&conn_iter);
>  
> -	/* Default to 24bit if no connector or format found. */
> -	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
> +	/* Default to 18bit if no connector or format found. */
> +	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_18BIT_666_RGB_1, DPI_FORMAT);
>  
>  	if (connector) {
>  		if (connector->display_info.num_bus_formats) {
>
Dave Stevenson Oct. 17, 2022, 5:03 p.m. UTC | #2 
Hi Laurent

On Sat, 15 Oct 2022 at 18:14, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Maxime (and Dave),
>
> Thank you for the patch.
>
> On Thu, Oct 13, 2022 at 11:56:50AM +0200, Maxime Ripard wrote:
> > From: Dave Stevenson <dave.stevenson@raspberrypi.com>
> >
> > DPI hasn't really been used up until now, so the default has
> > been meaningless.
> > In theory we should be able to pass the desired format for the
> > adjacent bridge chip through, but framework seems to be missing
> > for that.
>
> Doesn't the bridge infrastructure allow that ? Or maybe this commit
> message was written a while ago, before it was possible ?

Infrastructure may do, but it isn't always implemented.
Rightly or wrongly, the driver is currently finding the associated
connector, as commented as [1].

The main chain I'm looking is:
vc4_dpi -> dumb-vga-dac -> vga-connector
Unless I'm missing something, nothing in that chain defines the format
for the output. vga-connector (display-connector driver) tries to ask
the previous bridge for formats via atomic_get_output_bus_fmts and
atomic_get_input_fmts, but dumb-vga-dac (simple-bridge) doesn't
implement them.
So even if we tried following the chain it dies due to , and currently
the connector has no bus_formats defined in display_info, hence we end
up needing a default.
(Why do I get deja vu with panel-dpi and bus-format discussions?!)

Panels are fine as they do generally have a bus_format defined in display_info.

[1] https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/vc4/vc4_dpi.c#L139

> In any case, it would be nice to use the bus format exposed by the next
> bridge in the chain, but that can be done in a subsequent step. The new
> default seems reasonable.

I'll add having a look at atomic_get_output_bus_fmts and
atomic_get_input_fmts to my list of tasks again.

  Dave

> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>
> > As the main device to use DPI is the VGA666 or Adafruit Kippah,
> > both of which use RGB666, change the default to being RGB666 instead
> > of RGB888.
> >
> > Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > ---
> >  drivers/gpu/drm/vc4/vc4_dpi.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
> > index ecbe4cd87036..fdae02760b6d 100644
> > --- a/drivers/gpu/drm/vc4/vc4_dpi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_dpi.c
> > @@ -150,8 +150,8 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
> >       }
> >       drm_connector_list_iter_end(&conn_iter);
> >
> > -     /* Default to 24bit if no connector or format found. */
> > -     dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
> > +     /* Default to 18bit if no connector or format found. */
> > +     dpi_c |= VC4_SET_FIELD(DPI_FORMAT_18BIT_666_RGB_1, DPI_FORMAT);
> >
> >       if (connector) {
> >               if (connector->display_info.num_bus_formats) {
> >
>
> --
> Regards,
>
> Laurent Pinchart
diff mbox series

Patch

diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
index ecbe4cd87036..fdae02760b6d 100644
--- a/drivers/gpu/drm/vc4/vc4_dpi.c
+++ b/drivers/gpu/drm/vc4/vc4_dpi.c
@@ -150,8 +150,8 @@  static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 	}
 	drm_connector_list_iter_end(&conn_iter);
 
-	/* Default to 24bit if no connector or format found. */
-	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
+	/* Default to 18bit if no connector or format found. */
+	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_18BIT_666_RGB_1, DPI_FORMAT);
 
 	if (connector) {
 		if (connector->display_info.num_bus_formats) {