UAPI Re: [PATCH 1/3] drm: Add DRM_MODE_TV_MODE_MONOCHROME

[Maxime Ripard]

Hi,

On Tue, Feb 27, 2024 at 09:51:06AM +0000, Simon Ser wrote:
> On Monday, February 26th, 2024 at 18:23, Dave Stevenson <dave.stevenson at raspberrypi.com> wrote:
> > > and I've also completely missed any kernel command line
> > > arguments manipulating KMS properties.
> > 
> > "tv_mode" on the command line is handled in
> > drm_mode_parse_cmdline_options() [3], as are rotate, reflect_x,
> > reflect_y, margin_[left|right|top|bottom], and panel_orientation all
> > to set the relevant KMS properties.
> > 
> > Having "video=Composite-1:PAL,tv_mode=Mono" on the kernel command line
> > will set up connector Composite-1 with the standard 720x576 50Hz
> > interlaced timings, and DRM_MODE_TV_MODE_MONOCHROME selected on the
> > tv_mode property. Swap in different tv_mode descriptions as required
> > (eg PAL,tv_mode=SECAM), although some make little sense.
> > 
> > That's the main route I'm looking at for configuring this property,
> > for situations such as having a black and white TV connected. You
> > don't get the opportunity to interrogate a composite display over what
> > it supports, so it has to be configured manually somewhere in the
> > system. If your monitor doesn't support the system default, then you
> > can't see a GUI in order to change the option, and there is no
> > guaranteed supported configuration so the command line is about the
> > only option.
> > 
> > The use cases for runtime switching of the "tv_mode" are exceedingly
> > rare, so IMHO the property doesn't need exposing through the UAPI.
> > However it was added to the UAPI about 8 years ago for vc4 and sunxi,
> > and is also now used by other drivers, so can't be reverted. Does that
> > mean it can now never be changed without jumping through the hoop of
> > creating some userspace user?
> 
> I don't know what the rules were 8 years ago, but the current uAPI rules
> are what they are, and a new enum entry is new uAPI.

TBF, and even if the wayland compositors support is missing, this
property is perfectly usable as it is with upstream, open-source code,
through either the command-line or X.org, and it's documented.

So it's fine by me from a UAPI requirement side.

Maxime
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