linux-kernel - [PATCH v8 10/11] drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC

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Message-Id: <20210524165920.v8.10.I9330684c25f65bb318eff57f0616500f83eac3cc@changeid>
Date:   Mon, 24 May 2021 17:01:58 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     linux-arm-msm@...r.kernel.org, Linus W <linus.walleij@...aro.org>,
        Lyude Paul <lyude@...hat.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Steev Klimaszewski <steev@...i.org>, robdclark@...omium.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thierry Reding <treding@...dia.com>,
        dri-devel@...ts.freedesktop.org,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Robert Foss <robert.foss@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v8 10/11] drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC

This is really just a revert of commit 58074b08c04a ("drm/bridge:
ti-sn65dsi86: Read EDID blob over DDC"), resolving conflicts.

The old code failed to read the EDID properly in a very important
case: before the bridge's pre_enable() was called. The way things need
to work:
1. Read the EDID.
2. Based on the EDID, decide on video settings and pixel clock.
3. Enable the bridge w/ the desired settings.

The way things were working:
1. Try to read the EDID but fail; fall back to hardcoded values.
2. Based on hardcoded values, decide on video settings and pixel clock.
3. Enable the bridge w/ the desired settings.
4. Try again to read the EDID, it works now!
5. Realize that the hardcoded settings weren't quite right.
6. Disable / reenable the bridge w/ the right settings.

The reasons for the failures were twofold:
a) Since we never ran the bridge chip's pre-enable then we never set
   the bit to ignore HPD. This meant the bridge chip didn't even _try_
   to go out on the bus and communicate with the panel.
b) Even if we fixed things to ignore HPD, the EDID still wouldn't read
   if the panel wasn't on.

Instead of reverting the code, we could fix it to set the HPD bit and
also power on the panel. However, it also works nicely to just let the
panel code read the EDID. Now that we've split the driver up we can
expose the DDC AUX channel bus to the panel node. The panel can take
charge of reading the EDID.

NOTE: in order for things to work, anyone that needs to read the EDID
will need to instantiate their panel using the new DP AUX bus (AKA by
listing their panel under the "aux-bus" node of the bridge chip in the
device tree).

In the future if we want to use the bridge chip to provide a full
external DP port (which won't have a panel) then we will have to
conditinally add EDID reading back in.

Suggested-by: Andrzej Hajda <a.hajda@...sung.com>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
---

(no changes since v7)

Changes in v7:
- Adjusted commit message to talk about DP AUX bus.

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 22 ----------------------
 1 file changed, 22 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 5263206792f6..b7453c80cdb8 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -126,7 +126,6 @@
  * @connector:    Our connector.
  * @host_node:    Remote DSI node.
  * @dsi:          Our MIPI DSI source.
- * @edid:         Detected EDID of eDP panel.
  * @refclk:       Our reference clock.
  * @panel:        Our panel.
  * @enable_gpio:  The GPIO we toggle to enable the bridge.
@@ -157,7 +156,6 @@ struct ti_sn65dsi86 {
 	struct drm_dp_aux		aux;
 	struct drm_bridge		bridge;
 	struct drm_connector		connector;
-	struct edid			*edid;
 	struct device_node		*host_node;
 	struct mipi_dsi_device		*dsi;
 	struct clk			*refclk;
@@ -406,24 +404,6 @@ connector_to_ti_sn65dsi86(struct drm_connector *connector)
 static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector)
 {
 	struct ti_sn65dsi86 *pdata = connector_to_ti_sn65dsi86(connector);
-	struct edid *edid = pdata->edid;
-	int num, ret;
-
-	if (!edid) {
-		pm_runtime_get_sync(pdata->dev);
-		edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc);
-		pm_runtime_put_autosuspend(pdata->dev);
-	}
-
-	if (edid && drm_edid_is_valid(edid)) {
-		ret = drm_connector_update_edid_property(connector, edid);
-		if (!ret) {
-			num = drm_add_edid_modes(connector, edid);
-			if (num)
-				return num;
-		}
-	}
-
 	return drm_panel_get_modes(pdata->panel, connector);
 }

@@ -1356,8 +1336,6 @@ static void ti_sn_bridge_remove(struct auxiliary_device *adev)
 		mipi_dsi_device_unregister(pdata->dsi);
 	}

-	kfree(pdata->edid);
-
 	drm_bridge_remove(&pdata->bridge);

 	of_node_put(pdata->host_node);
-- 
2.31.1.818.g46aad6cb9e-goog