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My understanding was that fbdev is deprecated (but I was unable to find good info on this) and that one should use dumb buffers (https://manpages.debian.org/tes

by ablu 6y ago

My understanding was that fbdev is deprecated (but I was unable to find good info on this) and that one should use dumb buffers (https://manpages.debian.org/testing/libdrm-dev/drm-memory.7.en.html https://manpages.debian.org/testing/libdrm-dev/drm-memory.7....) for this simple stuff / somewhat portable software rendering. At least Qt allows to do this for embedded devices without hardware rendering.

joezydeco 6y ago
Embedded developers still need fbdev. There are lots of display-enabled SoCs that don't have or need a GPU.
- zozbot234 6y ago
  But even then, not every display-enabled SoC is well modeled as a dumb framebuffer. The Raspberry Pi itself provides hardware overlays, and it's quite problematic to expose them under that kind of model. The DRM infrastructure seems to be a lot more general and flexible.
  - joezydeco 6y ago
    I wouldn't recommend an RPi for product development. There are better SoCs, like i.MX, with documented graphics pipelines and graphic/video/camera overlays that are easy to use.
    - jschwartzi 6y ago
      Incidentally, i.MX6 is an example of using the Linux fbdev with hardware acceleration.
Jasper_ 6y ago
Yes. fbdev is kept alive for compatibility (and fbcon) reasons, but it's a really outdated API and drivers have to jump through hoops to support it. Please use dumb buffers when necessary. See a simple example here: https://github.com/magcius/drmdemo https://github.com/magcius/drmdemo
- nitrogen 6y ago
  Does the Nvidia proprietary kernel module provide a DRI interface?
  - Jasper_ 6y ago
    Yes, since a few years ago. https://download.nvidia.com/XFree86/Linux-x86_64/396.51/README/kms.html https://download.nvidia.com/XFree86/Linux-x86_64/396.51/READ...
- rowanG077 6y ago
  How can I write a simple device driver using dumb buffers? I have searched far and wide but I can't find anything. I'm forced to write a framebuffer driver. Once you dip into DRI shit get's insanely complex quick.
  - Jasper_ 6y ago
    For the simplest case, where you have contiguous memory for your framebuffer storage and no MMIO, try the CMA helpers: https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/drm_gem_cma_helper.c https://github.com/torvalds/linux/blob/master/drivers/gpu/dr... I wrote a basic device driver for a platform I worked on. It's since been upstreamed and gotten more eyeballs, but it's still relatively simple. https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/meson/meson_drv.c https://github.com/torvalds/linux/blob/master/drivers/gpu/dr...

by ablu 6y ago

joezydeco 6y ago

Embedded developers still need fbdev. There are lots of display-enabled SoCs that don't have or need a GPU.

zozbot234 6y ago
But even then, not every display-enabled SoC is well modeled as a dumb framebuffer. The Raspberry Pi itself provides hardware overlays, and it's quite problematic to expose them under that kind of model. The DRM infrastructure seems to be a lot more general and flexible.
- joezydeco 6y ago
  I wouldn't recommend an RPi for product development. There are better SoCs, like i.MX, with documented graphics pipelines and graphic/video/camera overlays that are easy to use.
  - jschwartzi 6y ago
    Incidentally, i.MX6 is an example of using the Linux fbdev with hardware acceleration.

Jasper_ 6y ago

Yes. fbdev is kept alive for compatibility (and fbcon) reasons, but it's a really outdated API and drivers have to jump through hoops to support it. Please use dumb buffers when necessary. See a simple example here: https://github.com/magcius/drmdemo https://github.com/magcius/drmdemo

nitrogen 6y ago
Does the Nvidia proprietary kernel module provide a DRI interface?
- Jasper_ 6y ago
  Yes, since a few years ago. https://download.nvidia.com/XFree86/Linux-x86_64/396.51/README/kms.html https://download.nvidia.com/XFree86/Linux-x86_64/396.51/READ...
rowanG077 6y ago
How can I write a simple device driver using dumb buffers? I have searched far and wide but I can't find anything. I'm forced to write a framebuffer driver. Once you dip into DRI shit get's insanely complex quick.
- Jasper_ 6y ago
  For the simplest case, where you have contiguous memory for your framebuffer storage and no MMIO, try the CMA helpers: https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/drm_gem_cma_helper.c https://github.com/torvalds/linux/blob/master/drivers/gpu/dr... I wrote a basic device driver for a platform I worked on. It's since been upstreamed and gotten more eyeballs, but it's still relatively simple. https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/meson/meson_drv.c https://github.com/torvalds/linux/blob/master/drivers/gpu/dr...