[PATCH v3 00/10] R-Car DU: LVDS dual-link mode support

Fri Jun 7 22:21:19 UTC 2019

Hi Kieran,

On Fri, Jun 07, 2019 at 11:16:37PM +0100, Kieran Bingham wrote:
> On 28/05/2019 15:12, Laurent Pinchart wrote:
> > Hello everybody,
> > 
> > This patch series implements support for LVDS dual-link mode in the
> > R-Car DU and R-Car LVDS encoder drivers, and well as in the thc63lvd1024
> > LVDS decoder driver.
> > 
> > LVDS dual-link is a mode of operation where two individual LVDS links
> > are operated together to carry even- and odd-numbered pixels separately.
> > This doubles the possible bandwidth of the video transmission. Both the
> > transmitter and the receiver need to support this mode of operation.
> > 
> > The R-Car D3 and E3 SoCs include two independent LVDS encoders that can
> > be grouped together to operate in dual-link mode. When used separately,
> > the LVDS encoders are connected to two different CRTCs and transmit
> > independent video streams. When used in dual-link mode, the first LVDS
> > encoder is connected to the first CRTC, and split even- and odd-numbered
> > pixels. It transmits half of the pixels on its LVDS output, and sends
> > the other half to the second LVDS encoder for transmittion over the
> > second LVDS link. The second LVDS encoder thus operates under control of
> > the first one, and isn't connected directly to a CRTC.
> > 
> > On the receiving side, the THC63LVD1024 LVDS-to-parallel bridge has two
> > LVDS inputs and two parallel outputs. It can operate in four different
> > modes:
> > 
> > - Single-in, single-out: The first LVDS input receives the video stream,
> >   and the bridge outputs it on the first parallel output. The second
> >   LVDS input and the second parallel output are not used.
> > 
> > - Single-in, dual-out: The first LVDS input receives the video stream,
> >   and the bridge splits even- and odd-numbered pixels and outputs them
> >   on the first and second parallel outputs. The second LVDS input is not
> >   used.
> > 
> > - Dual-in, single-out: The two LVDS inputs are used in dual-link mode,
> >   and the bridge combines the even- and odd-numbered pixels and outputs
> >   them on the first parallel output. The second parallel output is not
> >   used.
> > 
> > - Dual-in, dual-out: The two LVDS inputs are used in dual-link mode,
> >   and the bridge outputs the even- and odd-numbered pixels on the first
> >   parallel output.
> 
> Clarifying this, having checked with you, Dual-in, dual-out means 'even
> pixels are received on the first input, and provided on the first
> output, and odd pixels are received on the second input, and provided on
> the second output'.

Yes, my bad, this is wrong in the cover letter.

> > The operating mode is selected by two input pins of the bridge, which
> > are connected to DIP switches on the development boards I use. The mode
> > is thus fixed from a Linux point of view.
> 
> Would there ever by a scenario where these could be connected to GPIO's
> and changed dynamically? I guess that might not make much sense - as the
> configuration is more use case dependant.

This can't be ruled out, but the use cases would indeed be limited. If
the need ever arises, we can just extend the DT bindings to specify
those GPIOs, and add a new in-kernel API at the drm_bridge level to
configure the mode dynamically.

> > Patch 01/10 adds a new dual_link boolen field to the drm_bridge_timings
> > structure to let bridges report their LVDS mode of operation. Patch
> > 02/10 clarifies the THC63LVD1024 DT bindings to document dual-link
> > operation, and patch 03/10 implements dual-link support in the
> > thc64lvd1024 bridge driver by setting the drm_bridge_timings dual_link
> > field according to the mode selected through DT.
> > 
> > Patch 04/10 extends the R-Car LVDS DT bindings to specify the companion
> > LVDS encoder for dual-link operation. Patches 05/10 then performs a
> > small cleanup in the LVDS encoder driver. Patch 06/10 implements
> > dual-link support in the LVDS encoder driver, which involves retrieving
> > the operation mode from the LVDS receiver, locating the companion LVDS
> > encoder, and configuring both encoders when dual-link operation is
> > desired. The API towards the DU driver is also extended to report the
> > mode of operation.
> > 
> > Patch 07/10 implements dual-link mode support in the DU driver. There is
> > no specific configuration to be performed there, as dual-link is fully
> > implemented in the LVDS encoder driver, but the DU driver has to skip
> > creation of the DRM encoder and connector related to the second LVDS
> > encoder when dual-link is used, as the second LVDS encoder operates as a
> > slave of the first one, transparently from a CRTC (and thus userspace)
> > perspective.
> > 
> > Patch 08/10 specifies the companion LVDS encoder in the D3 and E3 DT
> > bindings. This by itself doesn't enable dual-link mode, the LVDS0
> > encoder is still connected to the HDMI output through LVDS receiver, and
> > the LVDS1 encoder is not used. Patches 09/10 and 10/10, not intended to
> > be merged, enable dual-link operation for the D3 and E3 boards for
> > testing and require flipping DIP switches on the boards.
> > 
> > The patches are based on top of my drm/du/next branch, and are available
> > for convenience at
> > 
> >         git://linuxtv.org/pinchartl/media.git drm/du/lvds/dual-link
> > 
> > They have been tested successfully on the D3 Draak board. I expect them
> > to work on E3 as well, but I don't have access to an Ebisu board to test
> > this.
> > 
> > Laurent Pinchart (10):
> >   drm: bridge: Add dual_link field to the drm_bridge_timings structure
> >   dt-bindings: display: bridge: thc63lvd1024: Document dual-link
> >     operation
> >   drm: bridge: thc63: Report input bus mode through bridge timings
> >   dt-bindings: display: renesas: lvds: Add renesas,companion property
> >   drm: rcar-du: lvds: Remove LVDS double-enable checks
> >   drm: rcar-du: lvds: Add support for dual-link mode
> >   drm: rcar-du: Skip LVDS1 output on Gen3 when using dual-link LVDS mode
> >   arm64: dts: renesas: r8a7799[05]: Point LVDS0 to its companion LVDS1
> >   [HACK] arm64: dts: renesas: draak: Enable LVDS dual-link operation
> >   [HACK] arm64: dts: renesas: ebisu: Enable LVDS dual-link operation
> > 
> >  .../bindings/display/bridge/renesas,lvds.txt  |   7 +
> >  .../display/bridge/thine,thc63lvd1024.txt     |   6 +
> >  .../arm64/boot/dts/renesas/r8a77990-ebisu.dts |  24 +++-
> >  arch/arm64/boot/dts/renesas/r8a77990.dtsi     |   2 +
> >  .../arm64/boot/dts/renesas/r8a77995-draak.dts |  24 +++-
> >  arch/arm64/boot/dts/renesas/r8a77995.dtsi     |   2 +
> >  drivers/gpu/drm/bridge/thc63lvd1024.c         |  54 ++++++--
> >  drivers/gpu/drm/rcar-du/rcar_du_encoder.c     |  12 ++
> >  drivers/gpu/drm/rcar-du/rcar_du_kms.c         |   2 +-
> >  drivers/gpu/drm/rcar-du/rcar_lvds.c           | 126 +++++++++++++-----
> >  drivers/gpu/drm/rcar-du/rcar_lvds.h           |   5 +
> >  include/drm/drm_bridge.h                      |   8 ++
> >  12 files changed, 214 insertions(+), 58 deletions(-)

-- 
Regards,

Laurent Pinchart