Message-ID: <20170512073509.ipbmqwng2vomv664@phenom.ffwll.local>
Date:   Fri, 12 May 2017 09:35:09 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Eric Anholt <eric@...olt.net>,
        Philippe Cornu <philippe.cornu@...com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Yannick Fertre <yannick.fertre@...com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v2 7/7] drm/atmel-hlcdc: Replace the panel usage with
 drm_panel_bridge.

On Thu, May 11, 2017 at 09:15:23PM +0200, Boris Brezillon wrote:
> 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.

Also note that we're getting ready to merge an entire pile of ->mode_valid
callbacks (from Jose Abreu), that should simplify this all a lot. With
that we could stuff the mode_valid code either into the encoder or the
crtc.
-Daniel

> 
> > 
> >  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
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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