Re: [PATCH v4 0/6] Cleanups for the nomodeset kernel command line parameter logic

[Pekka Paalanen]

On Mon, 8 Nov 2021 15:17:13 +0100
Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:

> Hi
> 
> Am 08.11.21 um 15:06 schrieb Javier Martinez Canillas:
> > 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.
> > 
> > This is a v4 of the patches, that address issues pointed out by Thomas
> > Zimmermann in v3: https://lkml.org/lkml/2021/11/8/384
> > 
> > Patch #1 and #2 are just trivial cleanups.
> > 
> > Patch #3 moves the nomodeset boot option to the DRM subsystem and renames
> > the variables and functions names.
> > 
> > Patch #4 removes the relationship between the nomodeset parameter and the
> > CONFIG_VGA_CONSOLE Kconfig symbol.
> > 
> > Patch #5 adds nomodeset to the kernel parameters documentation.
> > 
> > Patch #6 improves the message when nomodeset is enabled to make it more
> > accurate and less sensational.  
> 
> Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

Hi,

these ideas make sense to me, so FWIW,

Acked-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>

There is one nitpick I'd like to ask about:

+bool drm_get_modeset(void)
+{
+	return !drm_nomodeset;
+}
+EXPORT_SYMBOL(drm_get_modeset);

Doesn't "get" have a special meaning in the kernel land, like "take a
strong reference on an object and return it"?

As this is just returning bool without changing anything, the usual
word to use is "is". Since this function is also used at most once per
driver, which is rarely, it could have a long and descriptive name.

For example:

bool drm_is_modeset_driver_allowed(void);

- "drm" is the namespace
- "is" implies it is a read-only boolean inspection
- "modeset" is the feature being checked
- "driver" implies it is supposed gate driver loading or
  initialization, rather than modesets after drivers have loaded
- "allowed" says it is asking about general policy rather than what a
  driver does

Just a bikeshed, I'll leave it to actual kernel devs to say if this
would be more appropriate or worth it.


Thanks,
pq

> 
> Best regards
> Thomas
> 
> > 
> > Changes in v4:
> > - Don't mention the simpledrm driver and instead explain in high level
> >    terms what the nomodeset option is about.
> > - Don't mention DRM drivers in the kernel message and instead explain
> >    that only the system framebuffer will be available.
> > 
> > Changes in v3:
> > - Drop the drm_drv_enabled() function and just call to drm_get_modeset().
> > - Make drm_get_modeset() just a getter function and don't return an error.
> > - Move independent cleanups in drivers as separate preparatory patches.
> > 
> > Changes in v2:
> > - 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.
> > - 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.
> > 
> > Javier Martinez Canillas (6):
> >    drm: Don't print messages if drivers are disabled due nomodeset
> >    drm/vboxvideo: Drop CONFIG_VGA_CONSOLE guard to call
> >      vgacon_text_force()
> >    drm: Move nomodeset kernel parameter to the DRM subsystem
> >    drm: Decouple nomodeset from CONFIG_VGA_CONSOLE
> >    Documentation/admin-guide: Document nomodeset kernel parameter
> >    drm: Make the nomodeset message less sensational
> > 
> >   .../admin-guide/kernel-parameters.txt         |  7 ++++++
> >   drivers/gpu/drm/Kconfig                       |  6 +++++
> >   drivers/gpu/drm/Makefile                      |  2 ++
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       |  6 ++---
> >   drivers/gpu/drm/ast/ast_drv.c                 |  4 ++--
> >   drivers/gpu/drm/drm_nomodeset.c               | 24 +++++++++++++++++++
> >   drivers/gpu/drm/i915/i915_module.c            |  4 ++--
> >   drivers/gpu/drm/mgag200/mgag200_drv.c         |  4 ++--
> >   drivers/gpu/drm/nouveau/nouveau_drm.c         |  4 ++--
> >   drivers/gpu/drm/qxl/qxl_drv.c                 |  4 ++--
> >   drivers/gpu/drm/radeon/radeon_drv.c           | 10 +++-----
> >   drivers/gpu/drm/tiny/bochs.c                  |  4 ++--
> >   drivers/gpu/drm/tiny/cirrus.c                 |  5 ++--
> >   drivers/gpu/drm/vboxvideo/vbox_drv.c          |  6 ++---
> >   drivers/gpu/drm/virtio/virtgpu_drv.c          |  4 ++--
> >   drivers/gpu/drm/vmwgfx/vmwgfx_drv.c           |  4 ++--
> >   drivers/video/console/vgacon.c                | 21 ----------------
> >   include/drm/drm_mode_config.h                 |  2 ++
> >   include/linux/console.h                       |  6 -----
> >   19 files changed, 67 insertions(+), 60 deletions(-)
> >   create mode 100644 drivers/gpu/drm/drm_nomodeset.c
> >   
>

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