Merge branch 'for-next/block'

include: add SPDX GPL-2.0-only license tags for files without licensing information ...

According to our /README, GPL-2.0-only applies for the whole project
except noted otherwise.

Signed-off-by: Roland Hieber <rohieb@rohieb.name>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

block: Implement discard_range ...

This implements the discard_range hook. When a range of data is
discarded then we do not have to read it from the device and can
pass a zeroed buffer instead.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

block: Add flush callback ...

Some block devices need an explicit callback for flushing written
blocks. Add this callback.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

block: Collect block devices on list ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

block: implement block_read/block_write functions ...

Some drivers use blk->ops->read/write. This bypasses the caching block
layer and was never intended like this. The upper API to the block layer
is the cdev layer. This patch adds block_read and block_write functions
and uses them where appropriate.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

block: remove unused read_start and read_done ops ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

block: reimplement caching ...

The current caching layer only has a single buffer for
writing and reading. The FAT driver often accesses the
fat and then data again, which currently can't be cached.
Reimplement this with a list of cached chunks. The number
of chunks and their sizes are currently hardcoded, but
that could be easily made configurable.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

add block support ...

This adds a simple block layer to barebox. Reading and writing
to block devices can be painfully slow without caching, so
add a simple caching layer here.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>