linux-kernel - [PATCH v2 0/6] DSI/DBI, panel drivers, & tinyDRM v2

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Date:   Sat, 22 Aug 2020 18:32:44 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Noralf Tronnes <noralf@...nnes.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     od@...c.me, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Cercueil <paul@...pouillou.net>
Subject: [PATCH v2 0/6] DSI/DBI, panel drivers, & tinyDRM v2

Hi,

Here's a V2 of my patchset that attempts to clean up the current
situation with DSI/DBI panels drivers, and tinyDRM.

For the record, here is a small sum-up of the current situation:

- the current MIPI DBI code (drivers/gpu/drm/drm_mipi_dbi.c) is lagging
  way behind the MIPI DSI code (drivers/gpu/drm/drm_mipi_dsi.c). While
  the DSI code adds a proper bus support, with support for host drivers
  and client devices, there is no such thing with the DBI code. As such,
  it is currently impossible to write a standard DRM panel driver for a
  DBI panel.

- Even if the MIPI DBI code was updated with a proper bus, many panels
  and MIPI controllers support both DSI and DBI, so it would be a pain
  to support them without resolving to duplicating each driver.

- The panel drivers written against the DBI code are all "tinyDRM"
  drivers, which means that they will register a full yet simple DRM
  driver, and cannot be used as regular DRM panels for a different DRM
  driver.

- These "tinyDRM" drivers all use SPI directly, even though the panels
  they're driving can work on other interfaces (e.g. i8080 bus). Which
  means that one driver written for e.g. a ILI9341 would not work if
  the control interface is not SPI.

- The "tinyDRM" common code is entangled with DBI and there is no clear
  separation between the two. It could very well be moved to a single
  "tinyDRM" driver that works with a DRM panel obtained from devicetree,
  because the only requirement is that the panel supports a few given
  DCS commands.

Noteworthy changes since V1:

* The DT binding document for the NV3052C panel has been updated with
  the feedback I got from V1. It now supports multiple power supplies.

* Instead of using macros to define bus types, we now have an enum
  mipi_dcs_bus_type.

* The WARN_ONE_ONCE() that were in place to check that the host and
  client drivers provided the DCS bus bitmask is gone, we just default
  to DSI instead.

* DBI/SPI driver code was moved out of drivers/gpu/drm/bridge/.

* The DBI/SPI driver is registered as a driver by each client if needed,
  they just call module_mpi_dbi_spi_driver(). This addresses the issue
  in V1 that compatible strings had to be added to two different places.

* NV3052C and ILI9341 panel drivers were updated to remove custom
  backlight handling, call drm_panel_{disable,unprepare} on module exit,
  and various small fixes.

For a more detailed changelog, see the header of each individual patch.

Paul Cercueil (6):
  dt-bindings: display: Document NewVision NV3052C DT node
  drm: dsi: Let host and device specify supported bus
  drm: Add SPI DBI host driver
  drm/tiny: Add TinyDRM for DSI/DBI panels
  drm/panel: Add panel driver for NewVision NV3052C based LCDs
  drm/panel: Add Ilitek ILI9341 DBI panel driver

 .../display/panel/newvision,nv3052c.yaml      | 100 ++++
 drivers/gpu/drm/Kconfig                       |   8 +
 drivers/gpu/drm/Makefile                      |   1 +
 drivers/gpu/drm/drm_mipi_dbi_spi.c            | 247 +++++++++
 drivers/gpu/drm/drm_mipi_dsi.c                |   9 +
 drivers/gpu/drm/panel/Kconfig                 |  18 +
 drivers/gpu/drm/panel/Makefile                |   2 +
 drivers/gpu/drm/panel/panel-ilitek-ili9341.c  | 318 +++++++++++
 .../gpu/drm/panel/panel-newvision-nv3052c.c   | 510 ++++++++++++++++++
 drivers/gpu/drm/tiny/Kconfig                  |   8 +
 drivers/gpu/drm/tiny/Makefile                 |   1 +
 drivers/gpu/drm/tiny/tiny-dsi.c               | 266 +++++++++
 include/drm/drm_mipi_dbi_spi.h                |  42 ++
 include/drm/drm_mipi_dsi.h                    |  44 ++
 14 files changed, 1574 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/panel/newvision,nv3052c.yaml
 create mode 100644 drivers/gpu/drm/drm_mipi_dbi_spi.c
 create mode 100644 drivers/gpu/drm/panel/panel-ilitek-ili9341.c
 create mode 100644 drivers/gpu/drm/panel/panel-newvision-nv3052c.c
 create mode 100644 drivers/gpu/drm/tiny/tiny-dsi.c
 create mode 100644 include/drm/drm_mipi_dbi_spi.h

-- 
2.28.0