This page gives an overview of the DisplayPort driver which is available as part of the ZynqMP Linux distribution. The main driver is based on the Linux DRM KMS display subsystem. Additional drivers are based on other systems: DMA engine driver for DPDMA and ALSA driver for audio support.

Paths, files, links and documentation on this page are given relative to the Linux kernel source tree.
For information on the underlying hardware, see UG1085.

HW IP features

Features in bold are supported by the driver

Based on the VESA DisplayPort V.12a source-only specification.
Video support for the following:
° Resolution up to 4K x 2K at 30Fps.
° Y-only, YCbCr444, YCbCr422, YCbCr420, and RGB video formats.
° 6, 8, 10, or 12 bits per color components.
° Progressive video.
° A 36-bit native video input interface to capture live video.
° Non-live video from frame buffers using internal DPDMA.
Graphics support for the following:
° Non-live graphics from the frame buffer.
° 36-bit native video interface along with an 8-bit alpha channel to capture live graphics.
° 2-plane, on-the-fly rendering of video and graphics.
° Chroma upsampling.
° Chroma downsampling.
° Color space conversion from YCbCr to RGB and vice versa.
° Video blending.
° Chroma keying.
Audio support for the following:
° Up to two audio channels.
° Sample size of up to 24 bits.
° Maximum sample rate of 48 KHz.
° Live 24-bit audio from the PL.
° Non-live 16-bit audio from the frame buffer.
Audio mixer and volume control.
° Mixing of two audio streams of the same sampling rate and channel count.
° Provides gain control for audio streams.
Streaming A/V output back to the PL.
Includes a system time clock (STC) that is compliant with the ISO/IEC 13818-1 standard. Provides time stamping of the A/V presentation unit.

Missing Features, Known Issues and Limitations

Missing Features

This section summarizes the known issues and missing features (or experimental)

Live support is experimental feature
- Live input is supported as experimental (live input)
- Live output hasn't been fully verified
Pixel formats
- 12 bit YUV formats are not supported
Interop
- Some monitor may not sync reliably. Please refer to ZU+ supported monitors

Limitation

Both layers (drm planes) should be in the same size. Otherwise, if the requested size is different, the driver returns an error. This is hardware limitation.

Important AR links

ZU+ supported monitors

Note

The driver implementation has switched to the new driver in 2018.1, which supports new software features with more modular / scalable structure. The behavior of some APIs may be different, as well as the driver name from "xilinx_drm" to "xlnx".

Kernel Configuration

The dedicated DMA engine for DisplayPort should be enabled.
CONFIG_XILINX_DPDMA=y
The following config options are optional and required for audio support.
CONFIG_SOUND=y
CONFIG_SND=y
CONFIG_SND_SOC=y
CONFIG_SND_SOC_XILINX_DP=y
The driver, as some other multimedia drivers, needs CMA chunk. The following config options are recommended.
CONFIG_CMA=y
CONFIG_DMA_CMA=y
CONFIG_CMA_SIZE_MBYTES=256

The below is for new driver (>= 2018.1)
The following config options should be enabled in order to build the DisplayPort driver
CONFIG_DRM_XLNX=y
CONFIG_DRM_XLNX_BRIDGE=y
CONFIG_DRM_XLNX_BRIDGE_DEBUG_FS=y
CONFIG_DRM_ZYNQMP_DPSUB=y

The below is for old driver (< 2018.1)
The following config options should be enabled in order to build the DisplayPort driver
CONFIG_DRM=y
CONFIG_DRM_XILINX=y
CONFIG_DRM_XILINX_DP=y
CONFIG_DRM_XILINX_DP_SUB=y

Devicetree

The below is for new driver (>= 2018.1)
The snippet:
- zynqmp-display: zynqmp-display
The dt binding doc: Documentation/devicetree/bindings/display/xlnx/xlnx,zynqmp-dpsub.txt
- xlnx,zynqmp-dpsub.txt

The below is for old driver (< 2018.1)
Device tree nodes required are as below in "arch/arm64/boot/dts/xilinx/zynqmp.dtsi"
- Xilinx drm: xilinx drm node
- dp: dp
- dp subsystem: dp_sub
- dpdma: dpdma
For audio support
- alsa nodes: card, codec, pcm

For more details, Please refer to "Documentation/devicetree/bindings/drm/xilinx"
- dp.txt
- dp_sub.txt
- xilinx_drm.txt

Implementation

Power Management

The display pipeline is enabled and disabled upon the monitor HPD (hot plug detect) events. When there's disconnect event the DRM framework disables the pipeline. For the connect event the pipeline is enabled. The detect callback below from DP driver reports the connection status. This management is called DPMS (Display Power Management Signaling).

static enum drm_connector_status
zynqmp_dp_connector_detect(struct drm_connector *connector, bool force)
{
        if () {
                ....
                return connector_status_connected;
        }
 
disconnected:
        return connector_status_disconnected;
}

Upon the event, the DRM framework enables and disables the pipeline if possible. The below, the drm_kms_helper_hotplug_event() will disable or enable the fb console based on the event type.

bool drm_helper_hpd_irq_event(struct drm_device *dev)
{
                ...
                connector->status = drm_helper_probe_detect(connector, NULL, false);
                ....
 
        if (changed)
                drm_kms_helper_hotplug_event(dev);
 
        return changed;
}
EXPORT_SYMBOL(drm_helper_hpd_irq_event);

The event also goes into userspace through sysfs, so that any actively running application (ex, Xorg) can handle the event properly

void drm_kms_helper_hotplug_event(struct drm_device *dev)
{
        /* send a uevent + call fbdev */
        drm_sysfs_hotplug_event(dev);
        if (dev->mode_config.funcs->output_poll_changed)
                dev->mode_config.funcs->output_poll_changed(dev);
}
EXPORT_SYMBOL(drm_kms_helper_hotplug_event);

The userspace can handle the event. The below is the example of handling for Xorg,
https://github.com/Xilinx/meta-petalinux/blob/4e84d60865bf505d1ea425f3e5c84e37bf8f7455/recipes-core/udev/eudev/monitor-hotplug.sh

#!/bin/sh
#Adapt this script to your needs.
 
DEVICES=$(find /sys/class/drm/*/status)
 
#inspired by /etc/acpd/lid.sh and the function it sources
 
displaynum=`ls /tmp/.X11-unix/* | sed s#/tmp/.X11-unix/X##`
display=":$displaynum.0"
export DISPLAY=":$displaynum.0"
 
# from https://wiki.archlinux.org/index.php/Acpid#Laptop_Monitor_Power_Off
export XAUTHORITY=$(ps -C Xorg -f --no-header | sed -n 's/.*-auth //; s/ -[^ ].*//; p')
 
for i in /sys/class/drm/*/*/status ; do
status=$(cat $i);
connector=${i%/status*};
connector=${connector#*-};
if [ "$status" == "disconnected" ];
then
    xset dpms force off
elif [ "$status" == "connected" ];
then
    xset dpms force on
    if [ "$(xrandr | grep '\*')" = "" ];
    then
        xrandr --output $connector --auto
    fi
fi
done

At the driver level, when the pipeline is enabled / disabled, whatever necessary are notified (pmu fw) and enabled / disabled accordingly, including clock, dma, phy, and DP itself. Below is the enabling / disabling of display components such as clock, dma, and the IP. And enabling / disabling the encoder involves phy, connected monitor, transmitter,,,.

static void
zynqmp_disp_crtc_atomic_enable(struct drm_crtc *crtc,
                               struct drm_crtc_state *old_crtc_state)
{
        ...
 
        pm_runtime_get_sync(disp->dev);
        ret = zynqmp_disp_clk_enable(disp->pclk, &disp->pclk_en);
        if (ret) {
                dev_err(disp->dev, "failed to enable a pixel clock\n");
                return;
        }
        ...
        zynqmp_disp_enable(disp);
        ...
}

static void
zynqmp_disp_crtc_atomic_disable(struct drm_crtc *crtc,

Xilinx Wiki

ZynqMP DisplayPort Linux driver

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