[Intel-gfx] [RFC PATCH 0/7] drm/i915: add support for DisplayPort CEC-Tunneling-over-AUX

Mike Lothian mike at fireburn.co.uk
Thu May 25 15:30:09 UTC 2017


Hi

Sorry if this is off topic, I've got a Skylake Dell laptop with a USB-C
connector and no displayport

Which USB-C -> HDMI-2.0 connector do you recommend for stuff just working
based on your testing?

I've been putting off buying one until I knew 4K at 60Hz would work, CEC would
be nice to have too

Thanks

Mike

On Thu, 25 May 2017 at 16:06 Hans Verkuil <hverkuil at xs4all.nl> wrote:

> From: Hans Verkuil <hans.verkuil at cisco.com>
>
> This patch series adds support for the DisplayPort CEC-Tunneling-over-AUX
> protocol.
>
> This patch series is based on v4.12-rc2.
>
> The first four patches add support for a new CEC capability which is
> needed for these devices and for two helper functions.
>
> Then the DP CEC registers are added using Clint's patch.
>
> The core CEC tunneling support is added to drm_dp_cec.c.
>
> And finally this is hooked up in the i915 driver.
>
> Ideally the cec driver is created and destroyed whenever the DP-to-HDMI
> adapter is connected/disconnected, but I have not been a able to find
> a way to distinguish between connecting/disconnecting the HDMI cable
> and connecting/disconnecting the actual DP-to-HDMI adapter.
>
> My current approach is to check the CEC tunneling support whenever a new
> display is connected:
>
> - if CEC tunneling is supported, but no CEC adapter exists, then create
> one.
> - if CEC tunneling is not supported, then unregister the CEC adapter if one
>   was created earlier.
> - if CEC tunneling is supported and the capabilities are identical to the
>   existing CEC adapter, then leave it be.
> - if CEC tunneling is supported and the capabilities are different to the
>   existing CEC adapter, then unregister that CEC adapter and register a
>   new one.
>
> This works well, but it would be much nicer if I would just know when the
> DP adapter is disconnected as opposed to when the HDMI cable is
> disconnected
> from the adapter. Suggestions are welcome.
>
> The other remaining problem is that there are DP/USB-C to HDMI adapters
> that
> support CEC tunneling in the chipset, but where the CEC pin is simply never
> hooked up. From the point of view of the driver CEC is supported, but
> you'll
> never see any other devices.
>
> I am considering sending a CEC POLL message to logical address 0 (the TV)
> to detect if the CEC pin is connected, but this is not 100% guaranteed to
> work. This can be put under a kernel config option, though.
>
> I think I need to do something for this since of the 5 USB-C to HDMI
> adapters I've tested that set the CEC tunneling capability, only 2 have
> the CEC pin hooked up. So this seems to be quite common.
>
> I have tested this with my Intel NUC7i5BNK and with the two working
> USB-C to HDMI adapters that I have found:
>
> a Samsung EE-PW700 adapter and a Kramer ADC-U31C/HF adapter (I think that's
> the model, I need to confirm this).
>
> As usual the specifications of these adapters never, ever tell you whether
> this is supported or not :-( It's trial and error to find one that works.
> In
> fact, of the 10 USB-C to HDMI adapters I tested 5 didn't support CEC
> tunneling
> at all, and of the remaining 5 only two had the CEC pin hooked up and so
> actually worked.
>
> BTW, all adapters that supported CEC tunneling used the Parade PS176 chip.
>
> Output of cec-ctl -S (discovers the CEC topology):
>
> $ cec-ctl -S
> Driver Info:
>         Driver Name                : i915
>         Adapter Name               : DPDDC-C
>         Capabilities               : 0x0000007e
>                 Logical Addresses
>                 Transmit
>                 Passthrough
>                 Remote Control Support
>                 Monitor All
>         Driver version             : 4.12.0
>         Available Logical Addresses: 4
>         Physical Address           : 3.0.0.0
>         Logical Address Mask       : 0x0010
>         CEC Version                : 2.0
>         Vendor ID                  : 0x000c03 (HDMI)
>         OSD Name                   : 'Playback'
>         Logical Addresses          : 1 (Allow RC Passthrough)
>
>           Logical Address          : 4 (Playback Device 1)
>             Primary Device Type    : Playback
>             Logical Address Type   : Playback
>             All Device Types       : Playback
>             RC TV Profile          : None
>             Device Features        :
>                 None
>
>         System Information for device 0 (TV) from device 4 (Playback
> Device 1):
>                 CEC Version                : 1.4
>                 Physical Address           : 0.0.0.0
>                 Primary Device Type        : TV
>                 Vendor ID                  : 0x0000f0 (Samsung)
>                 OSD Name                   : TV
>                 Menu Language              : eng
>                 Power Status               : On
>
>         Topology:
>
>         0.0.0.0: TV
>             3.0.0.0: Playback Device 1
>
> Regards,
>
>         Hans
>
> Clint Taylor (1):
>   drm/cec: Add CEC over Aux register definitions
>
> Hans Verkuil (6):
>   cec: add CEC_CAP_NEEDS_HPD
>   cec-ioc-adap-g-caps.rst: document CEC_CAP_NEEDS_HPD
>   cec: add cec_s_phys_addr_from_edid helper function
>   cec: add cec_phys_addr_invalidate() helper function
>   drm: add support for DisplayPort CEC-Tunneling-over-AUX
>   drm/i915: add DisplayPort CEC-Tunneling-over-AUX support
>
>  .../media/uapi/cec/cec-ioc-adap-g-caps.rst         |   8 +
>  drivers/gpu/drm/Kconfig                            |   3 +
>  drivers/gpu/drm/Makefile                           |   1 +
>  drivers/gpu/drm/drm_dp_cec.c                       | 196
> +++++++++++++++++++++
>  drivers/gpu/drm/i915/Kconfig                       |  11 ++
>  drivers/gpu/drm/i915/intel_dp.c                    |  46 ++++-
>  drivers/media/cec/cec-adap.c                       |  34 +++-
>  drivers/media/cec/cec-api.c                        |   5 +-
>  drivers/media/cec/cec-core.c                       |   1 +
>  include/drm/drm_dp_helper.h                        |  83 +++++++++
>  include/media/cec.h                                |  15 ++
>  include/uapi/linux/cec.h                           |   2 +
>  12 files changed, 394 insertions(+), 11 deletions(-)
>  create mode 100644 drivers/gpu/drm/drm_dp_cec.c
>
> --
> 2.11.0
>
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