KodeMunkie/sm750hdmifb: Experimental Linux DRM/KMS driver for the SM750G10 SE-DP750A-HDMI, with HDMI, custom RGB565 dithering, DMA and software-scaled ultrawide modes. · GitHub

Push this card to real 2048-wide output or a software-scaled 2560×1080
ultrawide desktop, with bandwidth-saving colour conversion and update
optimisations for smoother performance.

Linux display driver for the single-HDMI SE-DP750A-HDMI PCIe card.

Experimental: this driver is for one specific SM750 board. Optional modes
can exceed published GPU or monitor clock limits and may produce no signal,
distortion, or an unstable display. Keep SSH or another recovery route
available when trying non-EDID modes.

The tested board is sold or marked as SE-DP750A-HDMI and has all of these:

• Silicon Motion SM750G10-AC, revision A1
• PCI ID 126f:0750
• Silicon Image/Lattice SiI9024ACNU HDMI transmitter
• 16 MiB display memory
• One HDMI output

The PCI ID alone is not enough. Other SM750 cards may use VGA, a different
transmitter, or different GPIO wiring and are not currently supported.

Ubuntu 24.04 and Linux Mint 22 users can build a DKMS package locally:

sudo apt update
sudo apt install build-essential dkms linux-headers-$(uname -r) libdrm-dev git
git clone https://github.com/KodeMunkie/sm750hdmifb.git
cd sm750hdmifb
make check
./build-package.sh
sudo apt install ./dist/sm750hdmifb_0.5.5_all.deb
sudo reboot

The reboot matters: it lets the package blacklist Linux’s old sm750fb driver
before it can claim the card. The package is named sm750hdmifb; the kernel
module is sm750hdmidrm.ko so it cannot be confused with sm750fb.ko.

The driver is intended for Linux 6.17 and newer. DKMS deliberately refuses
older kernels because the required DRM interfaces are not supported by this
project. The source has compatibility paths for Linux 6.17 through the 6.x
series and for Linux 7.0 onward. It currently builds and passes the full test
suite against 6.17 and 7.0 Ubuntu kernels; the manual CI workflow also builds
against Ubuntu 24.04’s 6.17 kernel headers.

There is no fixed upper version cap, but future kernels can change internal DRM
APIs. Because this is an out-of-tree driver, a new kernel version may require a
source update even though it falls within the intended 6.17+ range.

Prebuilt packages, when available, are published under
GitHub Releases.
Building locally is recommended because DKMS compiles against the installed
kernel headers.

By default the driver:

• Uses monitor EDID modes
• Uses dithered 16-bit RGB565 scanout
• Uses a hardware cursor
• Coalesces updates on a worker
• Uploads eight-row batches with DMA
• Falls back safely if DMA fails

Applications still render in 32-bit colour. Immediately before upload, the
driver converts changed screen regions to RGB565 and applies KodeMunkie’s
ordered dither with a 94% green-channel correction. This is the default because
the SM750 framebuffer is reached over a PCIe 1.1 x1 link. At the higher
resolutions that link cannot provide responsive full-screen 32-bit updates:
XRGB8888 sends four bytes per output pixel, while RGB565 sends two. Dithered
RGB565 therefore halves device-bound pixel traffic while preserving much of
the apparent colour detail.

Common kernel or GRUB options are:

The table omits the common sm750hdmidrm. prefix to keep it readable. For
example, enter enable_dma=0 as sm750hdmidrm.enable_dma=0 in GRUB.

Add options to the existing GRUB_CMDLINE_LINUX_DEFAULT value in
/etc/default/grub, then apply them with:

sudo update-grub
sudo reboot

Every option and its default is listed in
Module parameters.

The device is normally described as supporting up to 1920 pixels horizontally.
With edid_only=0, the driver also exposes these real 2048-wide hardware
modes:

softscale_wide=1 adds two wider logical desktops. Both require a physical
2560×1080 ultrawide monitor with FULL WIDESCREEN STRETCH ENABLED in its
on-screen menu:

For both modes, the HDMI signal is stretched from 2048x1080 to the physical
2560x1080 pixels of a 2K ultrawide monitor.

2048 pixels is the highest real width this card can produce in hardware.
The SM750 primary graphics plane has an 11-bit right-edge field, so its physical
scanout width cannot exceed 2048 pixels. This is a hardware constraint;
reducing the height does not release more horizontal bits. The 2464 and 2560
modes create wider workspaces in software, but the card still outputs only a
2048-pixel-wide signal.

An ultrawide monitor with its full-width or full-widescreen stretch option
enabled is required for the intended result. The complete path is:

logical desktop -> driver compression -> 2048x1080 HDMI -> monitor stretch to 2560x1080 physical pixels

The monitor’s stretch setting spatially expands the compressed 2048-pixel HDMI
image across all 2560 physical panel pixels. It is not recovering lost source
data, but it restores the intended ultrawide screen coverage and approximately
restores the intended aspect ratio. What looks “correct” is subjective because
the 2464 mode deliberately retains a small aspect difference.

For 2560x1080, the driver performs an optimized 5:4 reduction from 2560 to
2048 pixels, a 20% horizontal compression. A 2560-wide monitor then expands the
2048-pixel signal by 25% back across its panel. This provides a true
2560×1080-sized workspace, but some fine horizontal detail is necessarily
combined during the first step and more source pixels must be rendered and
processed.

For a physical 2560×1080 monitor, 2464x1080 is the recommended,
higher-performance and often sharper mode. It starts with
3.75% fewer desktop pixels and compresses width by only 16.9% before sending the
same 2048×1080 signal. The monitor still expands that signal across 2560 panel
pixels, so less source detail was discarded by the driver, but the final image
is about 3.9% wider than its logical geometry. This slight aspect distortion is
generally difficult to notice and is the tradeoff for improved responsiveness
and perceived sharpness. Enabling sm750hdmidrm.sharpen=1 is recommended.

Both wide modes can apply a small fixed 8% contrast sharpen after compression.
It restores some edge definition lost to filtering; it does not recreate
discarded pixels. The dither and green correction are applied during the final
RGB565 conversion before the 2048-wide scanout is uploaded.

This tested profile enables the driver mode catalogue and wide scaling:

DANGER: THIS PROFILE DISABLES EDID MODE RESTRICTIONS AND EXPOSES
EXPERIMENTAL OR ABOVE-SPECIFICATION CLOCKS. A LISTED MODE MAY BLANK OR
DESTABILIZE THE DISPLAY OR EXCEED A GPU, TRANSMITTER OR MONITOR LIMIT.

sm750hdmidrm.edid_only=0 sm750hdmidrm.softscale_wide=1 sm750hdmidrm.sharpen=1 sm750hdmidrm.scanout_format=rgb565-bbdither sm750hdmidrm.double_shadow=1 sm750hdmidrm.enable_dma=1

Some catalogue refresh rates run the SM750 DVO path or the monitor outside
published limits. A mode being listed does not guarantee that every monitor,
cable, KVM, or adapter will accept it. See
Modes and clock risks before experimenting.

rgb565-bbdither uses an 8×8 ordered dither conceived and tuned by KodeMunkie
specifically for desktop use on this card. It includes an adjustable
green-channel correction and anchors the pattern to screen coordinates, so
small updates do not make the pattern crawl or leave mismatched patches.

The three images below visualise the complete ultrawide conversion process.
Click any preview to open the original image. The logical desktop and physical
photo are shown at 50% page width. The compressed preview is shown at 41.56%,
preserving the 2048 / 2464 width reduction instead of stretching both digital
stages to the same preview width.

The driver receives this original 2464x1080 logical desktop.

The image above deliberately looks horizontally squashed. It reproduces the
2048x1080 HDMI scanout generated by compressing the 2464x1080 logical
desktop to the SM750’s hardware-width limit.

The photographed result fills the monitor’s 2560x1080 physical pixels at
75 Hz, using the driver’s 16-bit rgb565-bbdither dithered scanout.

The monitor’s FULL WIDESCREEN STRETCH option expands that signal across its
physical 2560x1080 panel. The complete path is therefore:

Logical desktop -> SM750 hardware scanout -> physical panel, stretched by the
monitor.

Check binding and recent driver messages:

lspci -nnk -d 126f:0750
journalctl -k -b | grep -iE 'sm750|sii902'

If an experimental mode gives no signal, boot an older kernel entry or remove
the added sm750hdmidrm.* GRUB options from recovery access. Testing and live
reload guidance is in Testing and recovery.

The official SM750 specification is known to be wrong for at least one
hardware-observed partial-update boundary. Empirically verified workarounds are
documented in the source and must not be removed solely because an ideal model
or specification says they are unnecessary.

The project is GPL-2.0-only. DDK-derived files came from Linux’s GPL-2.0
staging sm750fb driver. No proprietary Silicon Motion driver, binary object,
firmware blob, or closed library is included or linked. See the
provenance audit for details.

This project was created through extensive AI-assisted or “vibe coding”. I have
specified and physically tested the behaviour and designed the custom dither,
but do not claim enough Linux DRM, KMS, DKMS, or kernel-framework expertise to
independently guarantee every implementation detail. The source is published
for review and improvement, not as a claim of upstream kernel quality. Expert
review is welcome.

YOU USE THIS EXPERIMENTAL DRIVER AND EVERY NON-EDID OR ABOVE-SPECIFICATION
MODE ENTIRELY AT YOUR OWN RISK. YOU ARE RESPONSIBLE FOR RECOVERY ACCESS,
BACKUPS, MODE SELECTION AND HARDWARE COMPATIBILITY. THE AUTHORS AND
CONTRIBUTORS ARE NOT RESPONSIBLE FOR LOSS OF DISPLAY, DATA, TIME, HARDWARE,
INCOME OR ANY OTHER DIRECT OR INDIRECT LOSS.

The software is provided without warranty. See LICENSE.