Message-ID: <20170511211523.13fa866c@bbrezillon>
Date:   Thu, 11 May 2017 21:15:23 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Yannick Fertre <yannick.fertre@...com>,
        Philippe Cornu <philippe.cornu@...com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] drm/atmel-hlcdc: Replace the panel usage with
 drm_panel_bridge.

Hi Eric,

On Thu, 11 May 2017 11:31:28 -0700
Eric Anholt <eric@...olt.net> wrote:

> This cuts 135 lines of boilerplate, at the cost of losing the
> filtering of get_modes() using atmel_hlcdc_dc_mode_valid().  The
> atomic check will still check that we don't set an invalid mode,
> though.

Nice.

> 
> Signed-off-by: Eric Anholt <eric@...olt.net>

Acked-by: Boris Brezillon <boris.brezillon@...e-electrons.com>

A few comments below (no need to address them, those are just minor
things that can be fixed later on, or things I'm not comfortable
with but cannot be addressed easily).

> ---
> 
> This patch is just a proposal for atmel-hlcdc if you like it -- maybe
> you still want the filtering of get_modes().  I'm not sure from a
> userspace API perspective if we should really have the encoder (your
> CRTC's limits) filtering modes from a connector, but I'm also pretty
> sure it doesn't actually matter.

Actually I added this check because someone suggested it :-). I don't
think it's a real problem, and that should definitely be checked at the
CRTC level, not here.

> 
>  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c | 163 ++---------------------
>  1 file changed, 14 insertions(+), 149 deletions(-)
> 
> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c
> index 4b2cfbd0d43f..340ef962aa81 100644
> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c
> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c
> @@ -23,191 +23,56 @@
>  
>  #include <drm/drmP.h>
>  #include <drm/drm_of.h>
> +#include <drm/drm_bridge.h>
>  
>  #include "atmel_hlcdc_dc.h"
>  
> -/**
> - * Atmel HLCDC RGB connector structure
> - *
> - * This structure stores RGB slave device information.
> - *
> - * @connector: DRM connector
> - * @encoder: DRM encoder
> - * @dc: pointer to the atmel_hlcdc_dc structure
> - * @panel: panel connected on the RGB output
> - */
> -struct atmel_hlcdc_rgb_output {
> -	struct drm_connector connector;
> -	struct drm_encoder encoder;
> -	struct atmel_hlcdc_dc *dc;
> -	struct drm_panel *panel;
> -};
> -
> -static inline struct atmel_hlcdc_rgb_output *
> -drm_connector_to_atmel_hlcdc_rgb_output(struct drm_connector *connector)
> -{
> -	return container_of(connector, struct atmel_hlcdc_rgb_output,
> -			    connector);
> -}
> -
> -static inline struct atmel_hlcdc_rgb_output *
> -drm_encoder_to_atmel_hlcdc_rgb_output(struct drm_encoder *encoder)
> -{
> -	return container_of(encoder, struct atmel_hlcdc_rgb_output, encoder);
> -}
> -
> -static void atmel_hlcdc_rgb_encoder_enable(struct drm_encoder *encoder)
> -{
> -	struct atmel_hlcdc_rgb_output *rgb =
> -			drm_encoder_to_atmel_hlcdc_rgb_output(encoder);
> -
> -	if (rgb->panel) {
> -		drm_panel_prepare(rgb->panel);
> -		drm_panel_enable(rgb->panel);
> -	}
> -}
> -
> -static void atmel_hlcdc_rgb_encoder_disable(struct drm_encoder *encoder)
> -{
> -	struct atmel_hlcdc_rgb_output *rgb =
> -			drm_encoder_to_atmel_hlcdc_rgb_output(encoder);
> -
> -	if (rgb->panel) {
> -		drm_panel_disable(rgb->panel);
> -		drm_panel_unprepare(rgb->panel);
> -	}
> -}
> -
> -static const struct drm_encoder_helper_funcs atmel_hlcdc_panel_encoder_helper_funcs = {
> -	.disable = atmel_hlcdc_rgb_encoder_disable,
> -	.enable = atmel_hlcdc_rgb_encoder_enable,
> -};
> -
>  static const struct drm_encoder_funcs atmel_hlcdc_panel_encoder_funcs = {
>  	.destroy = drm_encoder_cleanup,
>  };
>  
> -static int atmel_hlcdc_panel_get_modes(struct drm_connector *connector)
> -{
> -	struct atmel_hlcdc_rgb_output *rgb =
> -			drm_connector_to_atmel_hlcdc_rgb_output(connector);
> -
> -	if (rgb->panel)
> -		return rgb->panel->funcs->get_modes(rgb->panel);
> -
> -	return 0;
> -}
> -
> -static int atmel_hlcdc_rgb_mode_valid(struct drm_connector *connector,
> -				      struct drm_display_mode *mode)
> -{
> -	struct atmel_hlcdc_rgb_output *rgb =
> -			drm_connector_to_atmel_hlcdc_rgb_output(connector);
> -
> -	return atmel_hlcdc_dc_mode_valid(rgb->dc, mode);
> -}
> -
> -static const struct drm_connector_helper_funcs atmel_hlcdc_panel_connector_helper_funcs = {
> -	.get_modes = atmel_hlcdc_panel_get_modes,
> -	.mode_valid = atmel_hlcdc_rgb_mode_valid,
> -};
> -
> -static enum drm_connector_status
> -atmel_hlcdc_panel_connector_detect(struct drm_connector *connector, bool force)
> -{
> -	struct atmel_hlcdc_rgb_output *rgb =
> -			drm_connector_to_atmel_hlcdc_rgb_output(connector);
> -
> -	if (rgb->panel)
> -		return connector_status_connected;
> -
> -	return connector_status_disconnected;
> -}
> -
> -static void
> -atmel_hlcdc_panel_connector_destroy(struct drm_connector *connector)
> -{
> -	struct atmel_hlcdc_rgb_output *rgb =
> -			drm_connector_to_atmel_hlcdc_rgb_output(connector);
> -
> -	if (rgb->panel)
> -		drm_panel_detach(rgb->panel);
> -
> -	drm_connector_cleanup(connector);
> -}
> -
> -static const struct drm_connector_funcs atmel_hlcdc_panel_connector_funcs = {
> -	.dpms = drm_atomic_helper_connector_dpms,
> -	.detect = atmel_hlcdc_panel_connector_detect,
> -	.fill_modes = drm_helper_probe_single_connector_modes,
> -	.destroy = atmel_hlcdc_panel_connector_destroy,
> -	.reset = drm_atomic_helper_connector_reset,
> -	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> -	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> -};
> -
>  static int atmel_hlcdc_attach_endpoint(struct drm_device *dev,
>  				       const struct device_node *np)
>  {
> -	struct atmel_hlcdc_dc *dc = dev->dev_private;
> -	struct atmel_hlcdc_rgb_output *output;
> +	struct drm_encoder *encoder;
>  	struct drm_panel *panel;
>  	struct drm_bridge *bridge;
>  	int ret;
>  
> -	output = devm_kzalloc(dev->dev, sizeof(*output), GFP_KERNEL);
> -	if (!output)
> +	encoder = devm_kzalloc(dev->dev, sizeof(*encoder), GFP_KERNEL);
> +	if (!encoder)
>  		return -EINVAL;
>  
> -	output->dc = dc;
> -
> -	drm_encoder_helper_add(&output->encoder,
> -			       &atmel_hlcdc_panel_encoder_helper_funcs);
> -	ret = drm_encoder_init(dev, &output->encoder,
> +	ret = drm_encoder_init(dev, encoder,
>  			       &atmel_hlcdc_panel_encoder_funcs,

atmel_hlcdc_panel_encoder_funcs should probably be renamed
atmel_hlcdc_dpi_encoder_funcs, but it's just a detail.

>  			       DRM_MODE_ENCODER_NONE, NULL);
>  	if (ret)
>  		return ret;
>  
> -	output->encoder.possible_crtcs = 0x1;
> +	encoder->possible_crtcs = 0x1;
>  
>  	ret = drm_of_find_panel_or_bridge(np, 0, 0, &panel, &bridge);
>  	if (ret)
>  		return ret;
>  
>  	if (panel) {
> -		output->connector.dpms = DRM_MODE_DPMS_OFF;
> -		output->connector.polled = DRM_CONNECTOR_POLL_CONNECT;
> -		drm_connector_helper_add(&output->connector,
> -				&atmel_hlcdc_panel_connector_helper_funcs);
> -		ret = drm_connector_init(dev, &output->connector,
> -					 &atmel_hlcdc_panel_connector_funcs,
> -					 DRM_MODE_CONNECTOR_Unknown);
> -		if (ret)
> -			goto err_encoder_cleanup;
> -
> -		drm_mode_connector_attach_encoder(&output->connector,
> -						  &output->encoder);
> -
> -		ret = drm_panel_attach(panel, &output->connector);
> -		if (ret) {
> -			drm_connector_cleanup(&output->connector);
> -			goto err_encoder_cleanup;
> -		}
> -
> -		output->panel = panel;
> +		bridge = drm_panel_bridge_add(panel, DRM_MODE_CONNECTOR_Unknown);
> +		if (IS_ERR(bridge))
> +			return PTR_ERR(bridge);

It would even be simpler if panels were directly registering
themselves to the bridge infrastructure so that they can be found with
drm_of_find_bridge() and we don't have to explicitly create this
bride->panel wrapper, but I remember that Thierry was not a big fan of
this idea.

Also, I keep thinking that we're abusing objects. A bridge is supposed
to convert a pixel stream in a given format/encoding into a different
format/encoding. Here, there's no conversion taking place in this
panel_bridge, it's just a way to expose the panel as a generic element
that can be easily connected to many display controller drivers.
To be perfectly clear, I really like this idea of providing a generic
wrapper, I'm just unsure exposing this wrapper as a bridge is such a
good idea, unless we clarify the meaning/goal of a 'drm_bridge' object.

The more I look at it, the more I think the drm_bridge is turning into a
generic element that is taking a stream of pixel in a specific format
and either consuming it of transforming it before forwarding it to the
next element in the chain.

Regards,

Boris

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