[PATCH v8 00/11] drm: Fix EDID reading on ti-sn65dsi86 by introducing the DP AUX bus

From: Douglas Anderson
Date: Mon May 24 2021 - 20:02:49 EST

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 a596fcd9cbc7
("drm/panel: panel-simple: Add missing
pm_runtime_dont_use_autosuspend() calls") on a sc7180-trogdor-lazor

At v8 now, the bindings patches have been beefed up from v7 and
review/ack tags were added. Also allmodconfig was fixed.

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
- Many patches had been landed, so only a few "controversial" ones

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.

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

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
dt-bindings: drm/aux-bus: Add an example
drm: Introduce the DP AUX bus
drm/panel: panel-simple: Allow panel-simple be a DP AUX endpoint
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
arm64: dts: qcom: sc7180-trogdor: Move panel under the bridge chip

.../bindings/display/bridge/ti,sn65dsi86.yaml | 20 +-
.../bindings/display/dp-aux-bus.yaml | 102 ++++++
.../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 | 111 ++++--
drivers/gpu/drm/drm_dp_aux_bus.c | 326 ++++++++++++++++++
drivers/gpu/drm/panel/Kconfig | 1 +
drivers/gpu/drm/panel/panel-simple.c | 64 +++-
include/drm/drm_dp_aux_bus.h | 57 +++
12 files changed, 665 insertions(+), 56 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