This driver is a reimplementation of matrix_keyboard, on which it
is heavily based: the former was made back in 2009 and then
lightly updated in 2012 to add some support for device-tree / OF.
It turns out that this is not enough, nor OF is fully supported,
as the global (or "clustered") interrupt is never probed, nor it
made usage of the GPIOD API which, nowadays, really simplifies
the job - but not only: it also provides means to set GPIO arrays
for controllers that are supporting this.
The latter is very important when dealing with slow GPIOs such as
I2C and/or SPI expanders (and, again, not only); by using the new
APIs everything fits the new systems, from simplifications of the
probe/remove functions to opening possibility of using expanders
to drive key matrices with or without protection diodes.
But then, why wasn't the old matrix_keyboard driver modified
instead of creating a new one?
The problem there is that the old driver is made to support the
old platform_device style and it's currently still being used by
some PXA boards that are not (yet?) ported to device-tree, so it
would be impossible to modernize it for good, which means that to
support GPIOD (which is - really - required for the aforementioned
reasons) and to fully support DT it would be necessary to wrap the
old GPIO API around the new GPIOD one, creating overhead and also
probably unnecessary memory usage, other than a very big driver
which, at least on embedded devices (having limited resources),
would be simply bad. Leaving the fact that I haven't got any old
board so it's impossible for me to analyze and optimize for them.
Since 98% of the users of the old driver are infact platforms that
have been ported to (or are born with) DT, the introduction of a
new driver that's purely made for them seemed to be the best
choice, also because the expectations are (I think) that all of
the old ARM-based boards will be ported to DT anyway, which will
actually deprecate the good old matrix_keyboard driver.
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
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