This page is to list kernel boot arguments related to the DRM KMS.

Overview

Some kernel boot arguments can be used to change settings / behavior of the Xilinx DRM KMS drivers. This page is to capture and describe available parameters.

Xilinx DRM KMS boot arguments

The Xilinx DRM KMS drivers have some specific module parameters.

  • xilinx_drm.fbdev_vres=2 : "fbdev virtual resolution multiplier for fb (default: 2)" This is to determine the virtual vertical resolution of the emulated fbdev buffer. The default value is 2 to enable double buffering. Higher value will allocate more memory.
  • xilinx_drm_dp.aux_timeout_ms=50 : "DP aux timeout value in msec (default: 50)" This value determines the timeout for aux transaction. Some monitors (ex, in specific power state) require longer timeout, then this value can be increased. But increasing it would result in more latency in the system level response.

Other kernel boot arguments

The descriptions of generic kernel parameters can be found in Documentation/kernel-parameters.txt of the kernel source tree (kernel-parameters.txt) . The below captures some descriptions.

  • cma=256M : The size and start/end address range for the CMA reserved area can be specified through this arguments. Note, the CMA area is shared for normal non-contiguous allocation (movable pages), but will come with some maintenance cost (ex, moving pages at allocation).
  • consoleblank=600 : The console blank (screen saver) timeout in seconds. Defaults to 10*60 = 10mins. A value of 0 disables the blank timer.
  • video=DP-1:1280x1024@60 : Frame buffer configuration. See Documentation/fb/modedb.txt. The command in this line will set the fbdev on DP-1 at 1280x1024@60 mode.

  • drm.debug=0 : "Enable debug output, where each bit enables a debug category.\n" Enable the debug messages from DRM core (ex, available bit values, 0x1, 0x2, 0x4, 0x8,0x10, 0x20)"
  • drm_kms_helper.fbdev_emulation=true : "Enable legacy fbdev emulation [default=true]" To enable / disable the fbdev emulation of DRM
  • drm_kms_helper.poll=true : Enable the periodic polling of the HPD / connection with a monitor.

Usage
The arguments / parameters can be given in the kernel bootargs.
bootargs "drm.debug=0x2f drm_kms_helper.fbdev_emulation=false"
Those are available in sysfs as module parameters. Each will have different access permission. Ones with write permission can change.
cat /sys/module/drm/parameters/debug
echo 0x2f > /sys/module/drm/parameters/debug

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