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Date:   Tue, 05 Oct 2021 20:09:07 -0700
From:   abhinavk@...eaurora.org
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Kalyan Thota <kalyan_t@...eaurora.org>,
        Kuogee Hsieh <khsieh@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [Freedreno] [PATCH v4 4/7] drm/msm/dp: Allow attaching a
 drm_panel

On 2021-10-05 19:09, Bjorn Andersson wrote:
> On Tue 05 Oct 17:35 PDT 2021, abhinavk@...eaurora.org wrote:
> 
>> Hi Bjorn
>> 
>> On 2021-10-05 16:13, Bjorn Andersson wrote:
>> > eDP panels might need some power sequencing and backlight management,
>> > so make it possible to associate a drm_panel with an eDP instance and
>> > prepare and enable the panel accordingly.
>> >
>> > Now that we know which hardware instance is DP and which is eDP,
>> > parser->parse() is passed the connector_type and the parser is limited
>> > to only search for a panel in the eDP case.
>> >
>> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>> > ---
>> >
>> > Changes since v3:
>> > - Previously posted separately, now added to series
>> > - Make the search for a panel conditional on it being an eDP connector
>> > - Move the search to of_graph port 1 (was 2 to distinguish from DP
>> > link to USB-C connector)
>> >
>> >  drivers/gpu/drm/msm/dp/dp_display.c |  9 ++++++---
>> >  drivers/gpu/drm/msm/dp/dp_display.h |  1 +
>> >  drivers/gpu/drm/msm/dp/dp_drm.c     | 11 +++++++++++
>> >  drivers/gpu/drm/msm/dp/dp_parser.c  | 30 ++++++++++++++++++++++++++++-
>> >  drivers/gpu/drm/msm/dp/dp_parser.h  |  3 ++-
>> >  5 files changed, 49 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c
>> > b/drivers/gpu/drm/msm/dp/dp_display.c
>> > index eaf08f9e7d87..bdaf227f05dc 100644
>> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
>> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>> > @@ -10,6 +10,7 @@
>> >  #include <linux/component.h>
>> >  #include <linux/of_irq.h>
>> >  #include <linux/delay.h>
>> > +#include <drm/drm_panel.h>
>> >
>> >  #include "msm_drv.h"
>> >  #include "msm_kms.h"
>> > @@ -230,12 +231,14 @@ static int dp_display_bind(struct device *dev,
>> > struct device *master,
>> >  	priv = drm->dev_private;
>> >  	priv->dp = &(dp->dp_display);
>> >
>> > -	rc = dp->parser->parse(dp->parser);
>> > +	rc = dp->parser->parse(dp->parser, dp->dp_display.connector_type);
>> >  	if (rc) {
>> >  		DRM_ERROR("device tree parsing failed\n");
>> >  		goto end;
>> >  	}
>> >
>> > +	dp->dp_display.panel_bridge = dp->parser->panel_bridge;
>> > +
>> >  	dp->aux->drm_dev = drm;
>> >  	rc = dp_aux_register(dp->aux);
>> >  	if (rc) {
>> > @@ -822,7 +825,7 @@ static int dp_display_set_mode(struct msm_dp
>> > *dp_display,
>> >  	return 0;
>> >  }
>> >
>> > -static int dp_display_prepare(struct msm_dp *dp)
>> > +static int dp_display_prepare(struct msm_dp *dp_display)
>> >  {
>> >  	return 0;
>> >  }
>> > @@ -896,7 +899,7 @@ static int dp_display_disable(struct
>> > dp_display_private *dp, u32 data)
>> >  	return 0;
>> >  }
>> >
>> > -static int dp_display_unprepare(struct msm_dp *dp)
>> > +static int dp_display_unprepare(struct msm_dp *dp_display)
>> >  {
>> >  	return 0;
>> >  }
>> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.h
>> > b/drivers/gpu/drm/msm/dp/dp_display.h
>> > index 02999408c052..24aefca66029 100644
>> > --- a/drivers/gpu/drm/msm/dp/dp_display.h
>> > +++ b/drivers/gpu/drm/msm/dp/dp_display.h
>> > @@ -15,6 +15,7 @@ struct msm_dp {
>> >  	struct device *codec_dev;
>> >  	struct drm_connector *connector;
>> >  	struct drm_encoder *encoder;
>> > +	struct drm_bridge *panel_bridge;
>> >  	bool is_connected;
>> >  	bool audio_enabled;
>> >  	bool power_on;
>> > diff --git a/drivers/gpu/drm/msm/dp/dp_drm.c
>> > b/drivers/gpu/drm/msm/dp/dp_drm.c
>> > index f33e31523f56..76856c4ee1d6 100644
>> > --- a/drivers/gpu/drm/msm/dp/dp_drm.c
>> > +++ b/drivers/gpu/drm/msm/dp/dp_drm.c
>> > @@ -5,6 +5,7 @@
>> >
>> >  #include <drm/drm_atomic_helper.h>
>> >  #include <drm/drm_atomic.h>
>> > +#include <drm/drm_bridge.h>
>> >  #include <drm/drm_crtc.h>
>> >
>> >  #include "msm_drv.h"
>> > @@ -160,5 +161,15 @@ struct drm_connector
>> > *dp_drm_connector_init(struct msm_dp *dp_display)
>> >
>> >  	drm_connector_attach_encoder(connector, dp_display->encoder);
>> >
>> > +	if (dp_display->panel_bridge) {
>> > +		ret = drm_bridge_attach(dp_display->encoder,
>> > +					dp_display->panel_bridge, NULL,
>> > +					DRM_BRIDGE_ATTACH_NO_CONNECTOR);
>> > +		if (ret < 0) {
>> > +			DRM_ERROR("failed to attach panel bridge: %d\n", ret);
>> > +			return ERR_PTR(ret);
>> > +		}
>> > +	}
>> > +
>> >  	return connector;
>> >  }
>> > diff --git a/drivers/gpu/drm/msm/dp/dp_parser.c
>> > b/drivers/gpu/drm/msm/dp/dp_parser.c
>> > index 4d6e047f803d..eb6bbfbea484 100644
>> > --- a/drivers/gpu/drm/msm/dp/dp_parser.c
>> > +++ b/drivers/gpu/drm/msm/dp/dp_parser.c
>> > @@ -6,6 +6,7 @@
>> >  #include <linux/of_gpio.h>
>> >  #include <linux/phy/phy.h>
>> >
>> > +#include <drm/drm_of.h>
>> >  #include <drm/drm_print.h>
>> >
>> >  #include "dp_parser.h"
>> > @@ -263,7 +264,28 @@ static int dp_parser_clock(struct dp_parser
>> > *parser)
>> >  	return 0;
>> >  }
>> >
>> > -static int dp_parser_parse(struct dp_parser *parser)
>> > +static int dp_parser_find_panel(struct dp_parser *parser)
>> > +{
>> > +	struct device *dev = &parser->pdev->dev;
>> > +	struct drm_panel *panel;
>> > +	int rc;
>> > +
>> > +	rc = drm_of_find_panel_or_bridge(dev->of_node, 1, 0, &panel, NULL);
>> > +	if (rc) {
>> > +		DRM_ERROR("failed to acquire DRM panel: %d\n", rc);
>> > +		return rc;
>> > +	}
>> > +
>> > +	parser->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
>> > +	if (IS_ERR(parser->panel_bridge)) {
>> > +		DRM_ERROR("failed to create panel bridge\n");
>> > +		return PTR_ERR(parser->panel_bridge);
>> > +	}
>> 
>> When we add a bridge using devm_drm_panel_bridge_add(), it will 
>> register
>> with default bridge functions which is fine
>> because we need the panel power to be controlled here.
>> 
>> 
>> 140 static const struct drm_bridge_funcs panel_bridge_bridge_funcs = {
>> 141 	.attach = panel_bridge_attach,
>> 142 	.detach = panel_bridge_detach,
>> 143 	.pre_enable = panel_bridge_pre_enable,
>> 144 	.enable = panel_bridge_enable,
>> 145 	.disable = panel_bridge_disable,
>> 146 	.post_disable = panel_bridge_post_disable,
>> 147 	.get_modes = panel_bridge_get_modes,
>> 
>> But what about the EDID related things, the DP/eDP driver already 
>> reads the
>> EDID and gets the modes so we need to skip
>> that in this case as otherwise it will end up calling the 
>> panel_get_modes in
>> the eDP panel which will be redundant.
>> 
>> Let me know if I am missing something in this proposal.
>> 
> 
> I'm slightly lost when it comes to these types, so can you please help
> me understand why the panel_bridge_bridge_funcs->get_modes() would be
> invoked with the proposed patches.
> 
> Because adding a log print in panel_bridge_get_modes() shows that it's
> not invoked.
> 
> 
> So I think we have the opposite problem, rather than having two
> redundant get_modes we only support relying on the EDID information
> directly in the DP driver, at this point.
> 
> So unless I'm missing something critical, this works and provides panel
> and backlight controls and the additional work to move the EDID read 
> out
> to the panel driver would better be done after this initial support
> lands?
> 
> Regards,
> Bjorn

I missed this line which uses the DRM_BRIDGE_ATTACH_NO_CONNECTOR

+		ret = drm_bridge_attach(dp_display->encoder,
+					dp_display->panel_bridge, NULL,
+					DRM_BRIDGE_ATTACH_NO_CONNECTOR);

In this case, no separate connector will get created and hence get_modes 
will not
be called again since this is just a virtual bridge. That explains why 
your log
didnt show up.

I will continue checking the rest of this patch.

> 
>> > +
>> > +	return 0;
>> > +}
>> > +
>> > +static int dp_parser_parse(struct dp_parser *parser, int
>> > connector_type)
>> >  {
>> >  	int rc = 0;
>> >
>> > @@ -284,6 +306,12 @@ static int dp_parser_parse(struct dp_parser
>> > *parser)
>> >  	if (rc)
>> >  		return rc;
>> >
>> > +	if (connector_type == DRM_MODE_CONNECTOR_eDP) {
>> > +		rc = dp_parser_find_panel(parser);
>> > +		if (rc)
>> > +			return rc;
>> > +	}
>> > +
>> >  	/* Map the corresponding regulator information according to
>> >  	 * version. Currently, since we only have one supported platform,
>> >  	 * mapping the regulator directly.
>> > diff --git a/drivers/gpu/drm/msm/dp/dp_parser.h
>> > b/drivers/gpu/drm/msm/dp/dp_parser.h
>> > index dac10923abde..3172da089421 100644
>> > --- a/drivers/gpu/drm/msm/dp/dp_parser.h
>> > +++ b/drivers/gpu/drm/msm/dp/dp_parser.h
>> > @@ -123,8 +123,9 @@ struct dp_parser {
>> >  	struct dp_display_data disp_data;
>> >  	const struct dp_regulator_cfg *regulator_cfg;
>> >  	u32 max_dp_lanes;
>> > +	struct drm_bridge *panel_bridge;
>> >
>> > -	int (*parse)(struct dp_parser *parser);
>> > +	int (*parse)(struct dp_parser *parser, int connector_type);
>> >  };
>> >
>> >  /**

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