[PATCH v9 00/11] drm: Fix EDID reading on ti-sn65dsi86 by introducing the DP AUX bus

[PATCH v9 00/11] drm: Fix EDID reading on ti-sn65dsi86 by introducing the DP AUX bus

[Douglas Anderson]

The primary goal of this series is to try to properly fix EDID reading
for eDP panels using the ti-sn65dsi86 bridge.

Previously we had a patch that added EDID reading but it turned out
not to work at bootup. This caused some extra churn at bootup as we
tried (and failed) to read the EDID several times and also ended up
forcing us to use the hardcoded mode at boot. With this patch series I
believe EDID reading is reliable at boot now and we never use the
hardcoded mode.

High level note: in this series the EDID reading is driven by the
panel driver, not by the bridge chip driver. I believe this makes a
reasonable amount of sense since the panel driver already _could_
drive reading the EDID if provided with the DDC bus and in future
planned work we'll want to give the panel driver the DDC bus (to make
decisions based on EDID) and the AUX bus (to control the
backlight). There are also planned patches from Laurent to make
ti-sn65dsi86 able to drive full DP monitors. In that case the bridge
chip will still be in charge of reading the EDID, but it's not hard to
make this dynamic.

This series is the logical successor to the 3-part series containing
the patch ("drm/bridge: ti-sn65dsi86: Properly get the EDID, but only
if refclk") [1].

This patch was tested against drm-misc-next commit 24994b91ecc5
("MAINTAINERS: Add maintainer for hyperv video device") on a
sc7180-trogdor-lazor device.

At v9 now this just had a few tiny tweaks / bugfixes. I also added a
patch to the end to make deferred probe a bit prettier. I _think_ this
series is now ready to land and seems to be fairly well-reviewed. I
believe all that's left is Laurent's official blessing that it's OK
for the panel to drive the EDID reading in this case.

Between v2 and v3, high-level view of changes:
- stop doing the EDID caching in the core.

Between v3 and v4, high-level view of changes:
- EDID reading is actually driven by the panel driver now. See above.
- Lots of chicken-and-egg problems solved w/ sub-devices.

Between v4 and v5, high-level view of changes.
- Some of the early patches landed, so dropped from series.
- New pm_runtime_disable() fix (fixed a patch that already landed).
- Added Bjorn's tags to most patches
- Fixed problems when building as a module.
- Reordered debugfs patch and fixed error handling there.
- Dropped last patch. I'm not convinced it's safe w/out more work.

Between v5 and v6, high-level view of changes:
- Added the patch ("drm/dp: Allow an early call to register DDC i2c
  bus")
- Many patches had been landed, so only a few "controversial" ones
  left.

Between v6 and v7, high-level view of changes:
- New AUX DP bus!

Between v7 and v8, high-level view of changes:
- More bindings work.
- Fixed allmodconfig.

Between v8 and v9, high-level view of changes:
- Fixed error/remove in panel.
- Properly handle of_node in sub-devices in sn65dsi86.
- Tiny bindings touchup including dropping "Example" patch.
- Added review tags.
- Added error message cleanup patch at the end.
- First patch (bugfix) dropped (it landed).

[1] https://lore.kernel.org/r/20210304155144.3.I60a7fb23ce4589006bc95c64ab8d15c74b876e68@changeid/

Changes in v9:
- ("Improve probe errors") patch new for v9.
- Commit message now notes aux-bus yaml won't have an "Example".
- Fix error handling / remove case when using AUX bus for DDC.
- Properly set the of_node of sn65dsi86 auxbus devices now.
- Rebased atop v9 ("Promote the AUX channel") patch.
- Use an absolute path to refer to aux-bus schema.

Changes in v8:
- Allow dp-aux-bus to be a module to fix allmodconfig builds
- Explain better why HPD needs to be in panel-simple in commit msg.
- Separate DP AUX bus binding is new for v8.
- ti-sn65dsi86 references the new aux bus bindings.

Changes in v7:
- Adjusted commit message to talk about DP AUX bus.
- Beefed up commit message in context of the DP AUX bus.
- List hpd properties bindings patch new for v7.
- Panel now under bridge chip instead of getting a link to ddc-i2c
- Patch introducing the DP AUX bus is new for v7.
- Patch to allow panel-simple to be DP AUX EP new for v7.
- Patch to support for DP AUX bus on ti-sn65dsi86 new for v7.
- Patch using the DP AUX for DDC new for v7.
- Remove use of now-dropped drm_dp_aux_register_ddc() call.
- Set the proper sub-device "dev" pointer in the AUX structure.
- ti-sn65dsi86: Add aux-bus child patch new for v7.

Changes in v6:
- Use new drm_dp_aux_register_ddc() calls.

Douglas Anderson (11):
  dt-bindings: display: simple: List hpd properties in panel-simple
  dt-bindings: drm: Introduce the DP AUX bus
  dt-bindings: drm/bridge: ti-sn65dsi86: Add aux-bus child
  drm: Introduce the DP AUX bus
  drm/panel: panel-simple: Allow panel-simple be a DP AUX endpoint
    device
  drm/panel: panel-simple: Stash DP AUX bus; allow using it for DDC
  drm/bridge: ti-sn65dsi86: Promote the AUX channel to its own sub-dev
  drm/bridge: ti-sn65dsi86: Add support for the DP AUX bus
  drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC
  drm/bridge: ti-sn65dsi86: Improve probe errors with dev_err_probe()
  arm64: dts: qcom: sc7180-trogdor: Move panel under the bridge chip

 .../bindings/display/bridge/ti,sn65dsi86.yaml |  20 +-
 .../bindings/display/dp-aux-bus.yaml          |  37 ++
 .../bindings/display/panel/panel-simple.yaml  |   2 +
 arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi  |  30 +-
 drivers/gpu/drm/Kconfig                       |   5 +
 drivers/gpu/drm/Makefile                      |   2 +
 drivers/gpu/drm/bridge/Kconfig                |   1 +
 drivers/gpu/drm/bridge/ti-sn65dsi86.c         | 129 +++----
 drivers/gpu/drm/drm_dp_aux_bus.c              | 326 ++++++++++++++++++
 drivers/gpu/drm/panel/Kconfig                 |   1 +
 drivers/gpu/drm/panel/panel-simple.c          |  68 +++-
 include/drm/drm_dp_aux_bus.h                  |  57 +++
 12 files changed, 594 insertions(+), 84 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/display/dp-aux-bus.yaml
 create mode 100644 drivers/gpu/drm/drm_dp_aux_bus.c
 create mode 100644 include/drm/drm_dp_aux_bus.h

-- 
2.32.0.rc1.229.g3e70b5a671-goog

[PATCH v9 01/11] dt-bindings: display: simple: List hpd properties in panel-simple

[Douglas Anderson]

The HPD (Hot Plug Detect) signal is present in many (probably even
"most") eDP panels. For eDP, this signal isn't actually used for
detecting hot-plugs of the panel but is more akin to a "panel ready"
signal. After you provide power to the panel, panel timing diagrams
typically say that you should wait for HPD to be asserted (or wait a
fixed amount of time) before talking to the panel.

The panel-simple bindings describes many eDP panels and many of these
panels provide the HPD signal. We should add the HPD-related
properties to the panel-simple bindings. The HPD properties are
actually defined in panel-common.yaml, so adding them here just
documents that they are OK for panels handled by the panel-simple
bindings.

NOTE: whether or not we'd include HPD properties in the panel node is
more a property of the board design than the panel itself. For most
boards using these eDP panels everything "magically" works without
specifying any HPD properties and that's been why we haven't needed to
allow the HPD properties earlier. On these boards the HPD signal goes
directly to a dedicated "HPD" input to the eDP controller and this
connection doesn't need to be described in the device tree. The only
time the HPD properties are needed in the device tree are if HPD is
hooked up to a GPIO or if HPD is normally on the panel but isn't used
on a given board. That means that if we don't allow the HPD properties
in panel-simple then one could argue that we've got to boot all eDP
panels (or at least all those that someone could conceivably put on a
system where HPD goes to a GPIO or isn't hooked up) from panel-simple.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
---

(no changes since v8)

Changes in v8:
- Explain better why HPD needs to be in panel-simple in commit msg.

Changes in v7:
- List hpd properties bindings patch new for v7.

 .../devicetree/bindings/display/panel/panel-simple.yaml         | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/panel/panel-simple.yaml b/Documentation/devicetree/bindings/display/panel/panel-simple.yaml
index b3797ba2698b..4a0a5e1ee252 100644
--- a/Documentation/devicetree/bindings/display/panel/panel-simple.yaml
+++ b/Documentation/devicetree/bindings/display/panel/panel-simple.yaml
@@ -298,6 +298,8 @@ properties:
   enable-gpios: true
   port: true
   power-supply: true
+  no-hpd: true
+  hpd-gpios: true
 
 additionalProperties: false
 
-- 
2.32.0.rc1.229.g3e70b5a671-goog

[PATCH v9 02/11] dt-bindings: drm: Introduce the DP AUX bus

[Douglas Anderson]

We want to be able to list an eDP panel as a child of an eDP
controller node to represent the fact that the panel is connected to
the controller's DP AUX bus. Though the panel and the controller are
connected in several ways, the DP AUX bus is the primary control
interface between the two and thus makes the most sense to model in
device tree hierarchy.

Listing a panel in this way makes it possible for the panel driver to
easily get access to the DP AUX bus that it resides on, which can be
useful to help in auto-detecting the panel and for turning on various
bits.

NOTE: historically eDP panels were _not_ listed under their controller
but were listed at the top level of the device tree. This will still
be supported for backward compatibility (and while DP controller
drivers are adapted to support the new DT syntax) but should be
considered deprecated since there is no downside to listing the panel
under the controller.

For now, the DP AUX bus bindings will only support an eDP panel
underneath. It's possible it could be extended to allow having a DP
connector under it in the future.

NOTE: there is no "Example" in this bindings file. Yikes! This avoids
duplicating the same example lots of places. See users of the aux bus
(like ti-sn65dsi86) for examples.

The idea for this bus's design was hashed out over IRC [1].

[1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2021-05-11

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
---

Changes in v9:
- Commit message now notes aux-bus yaml won't have an "Example".

Changes in v8:
- Separate DP AUX bus binding is new for v8.

 .../bindings/display/dp-aux-bus.yaml          | 37 +++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/dp-aux-bus.yaml

diff --git a/Documentation/devicetree/bindings/display/dp-aux-bus.yaml b/Documentation/devicetree/bindings/display/dp-aux-bus.yaml
new file mode 100644
index 000000000000..5e4afe9f98fb
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/dp-aux-bus.yaml
@@ -0,0 +1,37 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/dp-aux-bus.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: DisplayPort AUX bus
+
+maintainers:
+  - Douglas Anderson <dianders@chromium.org>
+
+description:
+  DisplayPort controllers provide a control channel to the sinks that
+  are hooked up to them. This is the DP AUX bus. Over the DP AUX bus
+  we can query properties about a sink and also configure it. In
+  particular, DP sinks support DDC over DP AUX which allows tunneling
+  a standard I2C DDC connection over the AUX channel.
+
+  To model this relationship, DP sinks should be placed as children
+  of the DP controller under the "aux-bus" node.
+
+  At the moment, this binding only handles the eDP case. It is
+  possible it will be extended in the future to handle the DP case.
+  For DP, presumably a connector would be listed under the DP AUX
+  bus instead of a panel.
+
+properties:
+  $nodename:
+    const: "aux-bus"
+
+  panel:
+    $ref: panel/panel-common.yaml#
+
+additionalProperties: false
+
+required:
+  - panel
-- 
2.32.0.rc1.229.g3e70b5a671-goog

[PATCH v9 03/11] dt-bindings: drm/bridge: ti-sn65dsi86: Add aux-bus child

[Douglas Anderson]

The patch ("dt-bindings: drm: Introduce the DP AUX bus") talks about
how using the DP AUX bus is better than learning how to slice
bread. Let's add it to the ti-sn65dsi86 bindings.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
---

Changes in v9:
- Use an absolute path to refer to aux-bus schema.

Changes in v8:
- ti-sn65dsi86 references the new aux bus bindings.

Changes in v7:
- ti-sn65dsi86: Add aux-bus child patch new for v7.

 .../bindings/display/bridge/ti,sn65dsi86.yaml | 20 ++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml
index 26932d2e86ab..12b876a20574 100644
--- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml
+++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml
@@ -70,6 +70,9 @@ properties:
     const: 1
     description: See ../../pwm/pwm.yaml for description of the cell formats.
 
+  aux-bus:
+    $ref: /schemas/display/dp-aux-bus.yaml#
+
   ports:
     $ref: /schemas/graph.yaml#/properties/ports
 
@@ -201,11 +204,26 @@ examples:
 
           port@1 {
             reg = <1>;
-            endpoint {
+            sn65dsi86_out: endpoint {
               remote-endpoint = <&panel_in_edp>;
             };
           };
         };
+
+        aux-bus {
+          panel {
+            compatible = "boe,nv133fhm-n62";
+            power-supply = <&pp3300_dx_edp>;
+            backlight = <&backlight>;
+            hpd-gpios = <&sn65dsi86_bridge 2 GPIO_ACTIVE_HIGH>;
+
+            port {
+              panel_in_edp: endpoint {
+                remote-endpoint = <&sn65dsi86_out>;
+              };
+            };
+          };
+        };
       };
     };
   - |
-- 
2.32.0.rc1.229.g3e70b5a671-goog

[PATCH v9 11/11] arm64: dts: qcom: sc7180-trogdor: Move panel under the bridge chip

[Douglas Anderson]

Putting the panel under the bridge chip (under the aux-bus node)
allows the panel driver to get access to the DP AUX bus, enabling all
sorts of fabulous new features.

While we're at this, get rid of a level of hierarchy for the panel
node. It doesn't need "ports / port" and can just have a "port" child.

For Linux, this patch has a hard requirement on the patches adding DP
AUX bus support to the ti-sn65dsi86 bridge chip driver. See the patch
("drm/bridge: ti-sn65dsi86: Add support for the DP AUX bus").

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
---

(no changes since v7)

Changes in v7:
- Panel now under bridge chip instead of getting a link to ddc-i2c

 arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 30 ++++++++++----------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
index 24d293ef56d7..c76afd857b54 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
@@ -260,21 +260,6 @@ max98357a: audio-codec-0 {
 		#sound-dai-cells = <0>;
 	};
 
-	panel: panel {
-		/* Compatible will be filled in per-board */
-		power-supply = <&pp3300_dx_edp>;
-		backlight = <&backlight>;
-		hpd-gpios = <&sn65dsi86_bridge 2 GPIO_ACTIVE_HIGH>;
-
-		ports {
-			port {
-				panel_in_edp: endpoint {
-					remote-endpoint = <&sn65dsi86_out>;
-				};
-			};
-		};
-	};
-
 	pwmleds {
 		compatible = "pwm-leds";
 		keyboard_backlight: keyboard-backlight {
@@ -674,6 +659,21 @@ sn65dsi86_out: endpoint {
 				};
 			};
 		};
+
+		aux-bus {
+			panel: panel {
+				/* Compatible will be filled in per-board */
+				power-supply = <&pp3300_dx_edp>;
+				backlight = <&backlight>;
+				hpd-gpios = <&sn65dsi86_bridge 2 GPIO_ACTIVE_HIGH>;
+
+				port {
+					panel_in_edp: endpoint {
+						remote-endpoint = <&sn65dsi86_out>;
+					};
+				};
+			};
+		};
 	};
 };
 
-- 
2.32.0.rc1.229.g3e70b5a671-goog

Re: [PATCH v9 02/11] dt-bindings: drm: Introduce the DP AUX bus

[Linus Walleij]

On Mon, Jun 7, 2021 at 7:06 PM Douglas Anderson <dianders@chromium.org> wrote:

> We want to be able to list an eDP panel as a child of an eDP
> controller node to represent the fact that the panel is connected to
> the controller's DP AUX bus. Though the panel and the controller are
> connected in several ways, the DP AUX bus is the primary control
> interface between the two and thus makes the most sense to model in
> device tree hierarchy.
>
> Listing a panel in this way makes it possible for the panel driver to
> easily get access to the DP AUX bus that it resides on, which can be
> useful to help in auto-detecting the panel and for turning on various
> bits.
>
> NOTE: historically eDP panels were _not_ listed under their controller
> but were listed at the top level of the device tree. This will still
> be supported for backward compatibility (and while DP controller
> drivers are adapted to support the new DT syntax) but should be
> considered deprecated since there is no downside to listing the panel
> under the controller.
>
> For now, the DP AUX bus bindings will only support an eDP panel
> underneath. It's possible it could be extended to allow having a DP
> connector under it in the future.
>
> NOTE: there is no "Example" in this bindings file. Yikes! This avoids
> duplicating the same example lots of places. See users of the aux bus
> (like ti-sn65dsi86) for examples.
>
> The idea for this bus's design was hashed out over IRC [1].
>
> [1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2021-05-11
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Rob Herring <robh@kernel.org>

I overall like this approach a lot:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

Re: [PATCH v9 03/11] dt-bindings: drm/bridge: ti-sn65dsi86: Add aux-bus child

[Linus Walleij]

On Mon, Jun 7, 2021 at 7:06 PM Douglas Anderson <dianders@chromium.org> wrote:

>  The patch ("dt-bindings: drm: Introduce the DP AUX bus") talks about
> how using the DP AUX bus is better than learning how to slice
> bread. Let's add it to the ti-sn65dsi86 bindings.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Rob Herring <robh@kernel.org>

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

Re: [PATCH v9 11/11] arm64: dts: qcom: sc7180-trogdor: Move panel under the bridge chip

[Bjorn Andersson]

On Mon 07 Jun 12:05 CDT 2021, Douglas Anderson wrote:

> Putting the panel under the bridge chip (under the aux-bus node)
> allows the panel driver to get access to the DP AUX bus, enabling all
> sorts of fabulous new features.
> 
> While we're at this, get rid of a level of hierarchy for the panel
> node. It doesn't need "ports / port" and can just have a "port" child.
> 
> For Linux, this patch has a hard requirement on the patches adding DP
> AUX bus support to the ti-sn65dsi86 bridge chip driver. See the patch
> ("drm/bridge: ti-sn65dsi86: Add support for the DP AUX bus").
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Acked-by: Linus Walleij <linus.walleij@linaro.org>

In case you want to merge this together with the driver changes
(even though there's no direct need for them to go together):

Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Regards,
Bjorn

> ---
> 
> (no changes since v7)
> 
> Changes in v7:
> - Panel now under bridge chip instead of getting a link to ddc-i2c
> 
>  arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 30 ++++++++++----------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> index 24d293ef56d7..c76afd857b54 100644
> --- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> @@ -260,21 +260,6 @@ max98357a: audio-codec-0 {
>  		#sound-dai-cells = <0>;
>  	};
>  
> -	panel: panel {
> -		/* Compatible will be filled in per-board */
> -		power-supply = <&pp3300_dx_edp>;
> -		backlight = <&backlight>;
> -		hpd-gpios = <&sn65dsi86_bridge 2 GPIO_ACTIVE_HIGH>;
> -
> -		ports {
> -			port {
> -				panel_in_edp: endpoint {
> -					remote-endpoint = <&sn65dsi86_out>;
> -				};
> -			};
> -		};
> -	};
> -
>  	pwmleds {
>  		compatible = "pwm-leds";
>  		keyboard_backlight: keyboard-backlight {
> @@ -674,6 +659,21 @@ sn65dsi86_out: endpoint {
>  				};
>  			};
>  		};
> +
> +		aux-bus {
> +			panel: panel {
> +				/* Compatible will be filled in per-board */
> +				power-supply = <&pp3300_dx_edp>;
> +				backlight = <&backlight>;
> +				hpd-gpios = <&sn65dsi86_bridge 2 GPIO_ACTIVE_HIGH>;
> +
> +				port {
> +					panel_in_edp: endpoint {
> +						remote-endpoint = <&sn65dsi86_out>;
> +					};
> +				};
> +			};
> +		};
>  	};
>  };
>  
> -- 
> 2.32.0.rc1.229.g3e70b5a671-goog
>