[RFC v2 0/8] Acer Chromebook R13 support

[matthias.bgg@gmail.com (Matthias Brugger)]

Hi Laurent,

On 10/17/2017 06:38 PM, Laurent Pinchart wrote:
> Hi Ulrich,
> 
> (CC'ing Matthias Brugger and Daniel Kurtz)
> 
> On Monday, 16 October 2017 18:31:32 EEST Ulrich Hecht wrote:
>> Hi!
>>
>> This is a new revision of the Acer Chromebook R13 support series. It does
>> not offer anything new in terms of functionality, but eliminates three out
>> of four ugly hacks and adds a few minor cleanups; see below for details.
>> Thanks to Robin Murphy and CK Hu for their comments and suggestions!
>>
>> I'm still looking for advice on how to implement the dual-role mmsys device
>> correctly; see "hack: mediatek: get mmsys to register as both DRM and clock
>> device" for details on this.
> 
> What I'd really like to find out is what the mmsys device is. Its DT binding
> documents it as "The Mediatek mmsys controller provides various clocks to the
> system". Even if it provides clocks to the display engine, it shouldn't be
> used as the root device in the display complex. There could of course be
> information I'm lacking as the datasheet isn't public. Hopefully someone from
> Mediatek and/or Google will be able to comment on this.
> 

Apart from enabling clock gates (in the clock driver) it provides the register 
space (config_regs) to other parts of the drm system, namely:
drivers/gpu/drm/mediatek/mtk_drm_crtc.c
drivers/gpu/drm/mediatek/mtk_drm_ddp.c

You can find the register table for mmsys in Part II here:
https://www.96boards.org/documentation/ConsumerEdition/MediaTekX20/AdditionalDocs/

Beware this document is for mt6797. Register offsets and values have changed (I 
just had a quick glance), but it gives you an idea what the driver does.

In the code path:
mtk_drm_crtc_atomic_enable -> mtk_crtc_ddp_hw_init -> mtk_ddp_add_comp_to_path
mtk_drm_ddp.c set's some bits in mmsys to enable the components. Which uses 
writel/readl_relaxed. This looks wrong, as mmsys is syscon and the driver should 
use regmap here.

I think we should add a new compatible for the display subsystem which accesses 
mmsys via a phandle and the correct regmap accessors. I'll try to submit a RFC 
to illustrate what I mean.

Regards,
Matthias

>> Like the previous revision, you can find this series at
>> https://github.com/uli/kernel/tree/elm-working, which also contains a config
>> file and several ancillary bits that are required to build a kernel
>> partition for the Chromebook. Instructions on how to do so (and various
>> other things that have to be done to get it running on your device) are
>> available at
>> https://www.elinux.org/User:Uli/Acer_Chromebook_R13_GPU_test_system (These
>> instructions have been written for the vendor kernel, but apply to mainline
>> as well, except that you won't need any extra patches.)
>>
>> CU
>> Uli
>>
>> Changes since RFC v1:
>> - cmdq: remove obsolete driver; not currently used anyway
>> - dt: remove CD GPIO from mmc1, does not seem to be correct
>> - mmc: remove mtk-sd.c revert hack (works fine without the CD pin)
>> - dsi: fix port number for drm_of_find_panel_or_bridge(), remove hack
>> - fbdev: add missing Signed-off-bys
>> - iommu: remove io-pgtable sanity check hack, has been properly fixed
>> - minor style fixes
>>
>>
>> Ulrich Hecht (8):
>>    drm/bridge: GPIO-controlled display multiplexer driver
>>    platform/chrome: ChromeOS firmware interface driver
>>    drm/bridge: Parade PS8640 MIPI DSI -> eDP converter driver
>>    drm/bridge: Analogix ANX7688 HDMI -> DP bridge driver
>>    arm64: dts: mediatek: Add Elm Rev. 3 device tree
>>    hack: mediatek: get mmsys to register as both DRM and clock device
>>    drm/mediatek: Add DRM-based framebuffer device
>>    drm: mediatek: Fix drm_of_find_panel_or_bridge conversion
>>
>>   arch/arm64/boot/dts/mediatek/Makefile            |    1 +
>>   arch/arm64/boot/dts/mediatek/mt8173-elm-rev3.dts |   21 +
>>   arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi     |  210 ++++
>>   arch/arm64/boot/dts/mediatek/mt8173-oak.dtsi     | 1013 +++++++++++++++++++
>>   drivers/clk/mediatek/clk-mt8173.c                |    4 +-
>>   drivers/gpu/drm/bridge/Kconfig                   |   32 +
>>   drivers/gpu/drm/bridge/Makefile                  |    5 +
>>   drivers/gpu/drm/bridge/analogix-anx7688.c        |  233 +++++
>>   drivers/gpu/drm/bridge/generic-gpio-mux.c        |  316 +++++++
>>   drivers/gpu/drm/bridge/parade-ps8640.c           | 1104 +++++++++++++++++++
>>   drivers/gpu/drm/mediatek/Makefile                |    2 +
>>   drivers/gpu/drm/mediatek/mtk_dpi.c               |    5 +-
>>   drivers/gpu/drm/mediatek/mtk_drm_ddp.c           |    5 +-
>>   drivers/gpu/drm/mediatek/mtk_drm_drv.c           |   15 +
>>   drivers/gpu/drm/mediatek/mtk_drm_drv.h           |    4 +-
>>   drivers/gpu/drm/mediatek/mtk_drm_fb.c            |   13 +
>>   drivers/gpu/drm/mediatek/mtk_drm_fb.h            |    3 +
>>   drivers/gpu/drm/mediatek/mtk_drm_fbdev.c         |  181 ++++
>>   drivers/gpu/drm/mediatek/mtk_drm_fbdev.h         |   32 +
>>   drivers/gpu/drm/mediatek/mtk_dsi.c               |    2 +-
>>   drivers/gpu/drm/mediatek/mtk_hdmi.c              |    5 +-
>>   drivers/platform/chrome/Kconfig                  |   18 +
>>   drivers/platform/chrome/Makefile                 |    2 +
>>   drivers/platform/chrome/chromeos.c               |  120 +++
>>   drivers/platform/chrome/chromeos.h               |   61 ++
>>   drivers/platform/chrome/chromeos_arm.c           |  264 ++++++
>>   drivers/platform/chrome/elog.h                   |  186 ++++
>>   include/linux/chromeos_platform.h                |   27 +
>>   28 files changed, 3874 insertions(+), 10 deletions(-)
>>   create mode 100644 arch/arm64/boot/dts/mediatek/mt8173-elm-rev3.dts
>>   create mode 100644 arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi
>>   create mode 100644 arch/arm64/boot/dts/mediatek/mt8173-oak.dtsi
>>   create mode 100644 drivers/gpu/drm/bridge/analogix-anx7688.c
>>   create mode 100644 drivers/gpu/drm/bridge/generic-gpio-mux.c
>>   create mode 100644 drivers/gpu/drm/bridge/parade-ps8640.c
>>   create mode 100644 drivers/gpu/drm/mediatek/mtk_drm_fbdev.c
>>   create mode 100644 drivers/gpu/drm/mediatek/mtk_drm_fbdev.h
>>   create mode 100644 drivers/platform/chrome/chromeos.c
>>   create mode 100644 drivers/platform/chrome/chromeos.h
>>   create mode 100644 drivers/platform/chrome/chromeos_arm.c
>>   create mode 100644 drivers/platform/chrome/elog.h
>>   create mode 100644 include/linux/chromeos_platform.h
> 
>