1. 14 Oct, 2022 1 commit
    • Thomas Zimmermann's avatar
      drm/ofdrm: Add ofdrm for Open Firmware framebuffers · c8a17756
      Thomas Zimmermann authored
      Open Firmware provides basic display output via the 'display' node.
      DT platform code already provides a device that represents the node's
      framebuffer. Add a DRM driver for the device. The display mode and
      color format is pre-initialized by the system's firmware. Runtime
      modesetting via DRM is not possible. The display is useful during
      early boot stages or as error fallback.
      
      Similar functionality is already provided by fbdev's offb driver,
      which is insufficient for modern userspace. The old driver includes
      support for BootX device tree, which can be found on old 32-bit
      PowerPC Macintosh systems. If these are still in use, the
      functionality can be added to ofdrm or implemented in a new
      driver. As with simpledrm, the fbdev driver cannot be selected if
      ofdrm is already enabled.
      
      Two notable points about the driver:
      
       * Reading the framebuffer aperture from the device tree is not
      reliable on all systems. Ofdrm takes the heuristics and a comment
      from offb to pick the correct range.
      
       * No resource management may be tied to the underlying PCI device.
      Otherwise the handover to the native driver will fail with a resource
      conflict. PCI management is therefore done as part of the platform
      device's cleanup.
      
      The driver has been tested on qemu's ppc64le emulation. The device
      hand-over has been tested with bochs.
      
      v5:
      	* use drm_atomic_helper_check_crtc_primary_plane()
      v4:
      	* set preferred depth to the correct value
      	* set bpp value for console emulation
      	* output scanout-buffer parameters with drm_dbg()
      v3:
      	* reintegrate FWFB helpers into ofdrm
      	* use damage iterator
      	* sync GEM BOs with drm_gem_fb_{begin,end}_cpu_access()
      	* fix various atomic_check helpers
      	* remove CRTC atomic_{enable,disable} (Javier)
      	* compute stride with drm_format_info_min_pitch() (Daniel)
      v2:
      	* removed simple-pipe helpers
      	* built driver on top of FWFB helpers
      	* merged all init code into single function
      	* make PCI support optional (Michal)
      	* support COMPILE_TEST (Javier)
      Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
      Reviewed-by: default avatarJavier Martinez Canillas <javierm@redhat.com>
      
      convert
      Link: https://patchwork.freedesktop.org/patch/msgid/20221011150712.3928-2-tzimmermann@suse.de
      c8a17756
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