"about.html" is available only for the alabaster theme [1].
Unconditionally putting it to html_sidebars prevents us from
using other themes which respect html_sidebars.

Remove about.html from the initialization and insert it at the
front for the alabaster theme.

Link: [1] https://alabaster.readthedocs.io/en/latest/installation.html#sidebars
Fixes: d5389d3145ef ("docs: Switch the default HTML theme to alabaster")
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/4b162dbe-2a7f-1710-93e0-754cf8680aae@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

The Sphinx 2.4 release is three years old, and it is becoming increasingly
difficult to even find a system with an sufficiently archaic Python
installation that can run versions older than that.  I can no longer test
changes against anything prior to 2.4.x.

Move toward raising our minimum Sphinx requirement to 2.4.x so we can
delete some older support code and claim to support a range of versions
that we can actually test.

In the absence of screams, the actual removal of support can happen later
in 2023.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

We love to nest our documenation for good structure, but that means
the table of contents needs to keep up or you can't navigate them.

Realized this trying to find the drm property documentation, which
with some shuffling around disappeared. Why I didn't realize we can do
this earlier, no idea.

Since the relevant parts of the toc are only loaded if you're in the
right .html file there's no harm in going all the way to unlimited.

Note that this has no impact on the alabaster theme (which has a much
simpler sidebar toc which doesn't show the entire hierarchy, only
what's in the local rendered file) nor on the various :toctree:
rendered inline in the output.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Link: https://lore.kernel.org/r/20221108115707.1232621-1-daniel.vetter@ffwll.ch
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

The alabaster theme likes to provide explicit sizes for fonts, which
overrides the users's own browser settings and is guaranteed to displease
folks.  Set the font size to "inherit" so that the users browser settings
control the font size they get.  We can use the font_size configuration
option for the main body font (changing the size I'd already put there),
but the sidebar size can only be set via custom CSS.

Reported-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Remove the ancient support for the Sphinx "classic" theme; everybody will
have alabaster, so that fallback is no longer needed.

While in the neighborhood: get rid of lots of useless comment lines.  They
describe the state of Sphinx options when we first created that file and
are just clutter now.

Suggested-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

This is just the beginning: tighten up the layout a bit to improve the
information density in the browser.  Also reconfigure the page width in
terms of character units (em) rather than pixels, making it more
display-independent.  To that end, add a custom.css file to
tweak Alabaster CSS settings.

Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

The read-the-docs theme is not entirely attractive and doesn't give us
control over the left column.  "Alabaster" is deemed the default Sphinx
theme, it is currently maintained and shipped bundled with Sphinx itself,
so there is no need to install it separately.  Switch over to this theme as
the default for building kernel documentation; the DOCS_THEME environment
variable can still be used to select a different theme.

Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Use the html_sidebars directive to get a more useful set of links in the
left column.

Unfortunately, this is a no-op with the default RTD theme, but others
observe it.

Reviewed-by: David Vernet <void@manifault.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20220927160559.97154-4-corbet@lwn.net
Signed-off-by: Jonathan Corbet <corbet@lwn.net>