[v2,0/2] Cleanups for the nomodeset kernel command line parameter logic

Message

Javier Martinez Canillas Nov. 4, 2021, 4:07 p.m. UTC

There is a lot of historical baggage on this parameter. It is defined in
the vgacon driver as nomodeset, but its set function is called text_mode()
and the value queried with a function named vgacon_text_force().

All this implies that it's about forcing text mode for VGA, yet it is not
used in neither vgacon nor other console driver. The only users for these
are DRM drivers, that check for the vgacon_text_force() return value to
determine whether the driver should be loaded or not.

That makes it quite confusing to read the code, because the variables and
function names don't reflect what they actually do and also are not in the
same subsystem as the drivers that make use of them.

This patch-set attempts to cleanup the code by moving the nomodseset param
to the DRM subsystem and do some renaming to make their intention clearer.

There is also another aspect that could be improved, and is the fact that
drivers are checking for the nomodeset being set as an indication if have
to be loaded.

But there may be other reasons why this could be the case, so it is better
to encapsulate the logic in a separate function to make clear what's about.

This is a v2 of the patches, that address the issues pointed out by Thomas
Zimmermann and Jani Nikula in v1:

https://lore.kernel.org/lkml/[e-mail]/T/

Patch #1 adds a drm_drv_enabled() function that could be used by drivers to
check if these could be enabled, instead of just using vgacon_text_force().

Patch #2 moves the nomodeset logic to the DRM subsystem and renames the
functions and variables to better explain what these actually do.

Changes in v2:
- Squash patch to add drm_drv_enabled() and make drivers use it.
- Make the drivers changes before moving nomodeset logic to DRM.
- Make drm_drv_enabled() return an errno and -ENODEV if nomodeset.
- Remove debug and error messages in drivers.
- Conditionally build drm_nomodeset.o if CONFIG_VGA_CONSOLE is set.
- Squash patches to move nomodeset logic to DRM and do the renaming.
- Name the function drm_check_modeset() and make it return -ENODEV.

Javier Martinez Canillas (2):
  drm: Add a drm_drv_enabled() to check if drivers should be enabled
  drm: Move nomodeset kernel parameter to the DRM subsystem

 drivers/gpu/drm/Makefile                |  2 ++
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c |  8 +++-----
 drivers/gpu/drm/ast/ast_drv.c           |  8 +++++---
 drivers/gpu/drm/drm_drv.c               | 21 ++++++++++++++++++++
 drivers/gpu/drm/drm_nomodeset.c         | 26 +++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_module.c      |  8 +++++---
 drivers/gpu/drm/mgag200/mgag200_drv.c   |  8 +++++---
 drivers/gpu/drm/nouveau/nouveau_drm.c   |  6 ++++--
 drivers/gpu/drm/qxl/qxl_drv.c           |  8 +++++---
 drivers/gpu/drm/radeon/radeon_drv.c     |  7 ++++---
 drivers/gpu/drm/tiny/bochs.c            |  8 +++++---
 drivers/gpu/drm/tiny/cirrus.c           |  9 ++++++---
 drivers/gpu/drm/vboxvideo/vbox_drv.c    | 10 +++++-----
 drivers/gpu/drm/virtio/virtgpu_drv.c    |  6 +++---
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c     |  6 +++---
 drivers/video/console/vgacon.c          | 21 --------------------
 include/drm/drm_drv.h                   |  1 +
 include/drm/drm_mode_config.h           |  6 ++++++
 include/linux/console.h                 |  6 ------
 19 files changed, 109 insertions(+), 66 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_nomodeset.c