Add a note about the pager to the console documentation, with some more
information in the developer section. Also include the pager API.
Series-to: concept
Cover-letter:
Introduce a pager for the console
Some U-Boot commands can produce a lot of output and this can run off
top of the display. This series introduces a simple pager feature, to
allow the output to be read, before pressing SPACE to continue.
A fixed buffer size (4K) is used, which sets a limit on the permmited
output before paging fails and the output is simply written all in one
lot. In most cases this is plenty, but 'env print' does print the whole
environment as one string, so if the legacy distro-boot scripts are used
it could happen.
The default number of visible lines is set with a Kconfig option. Where
a video terminal is being used, the page size is set to match that. In
general U-Boot cannot guess the number of visible lines, since a serial
terminal may be in use.
There is also a 'pager' environment variable which can override any
detected value.
This initial series only counts newlines. It has no support for counting
characters so the result will be sub-optimal if very long lines are
written. This could be addressed in a future patch.
Some effort is made to handle common cases correctly. For example, if
stdout is changed to a serial or vidconsole device, that is used to
determine the page length. When redirecting sandbox to a file, no
attempt is made.
Future work may detect the terminal size by sending an ANSI sequence.
END
Signed-off-by: Simon Glass <sjg@chromium.org>
Series-version: 2
10a0dec8bc